diff --git a/.eslintrc b/.eslintrc
index 6071ddc..066e1b5 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -2,6 +2,19 @@
     "extends": "airbnb-base",
     "rules": {
         "indent": ["error", 4],
-        "no-var": "error"
+        "no-var": "error",
+        "camelcase": 0,
+        "prefer-template": 0,
+        "no-param-reassign": 0,
+        "func-names": 0,
+        "one-var": 0,
+        "prefer-const": 0,
+        "no-nested-ternary": 0,
+        "no-else-return": 0,
+        "no-plusplus": 0,
+        "no-mixed-operators": 0,
+        "prefer-spread": 0,
+        "no-shadow": 0,
+        "no-underscore-dangle": 0,
     }
 }
diff --git a/Gruntfile.coffee b/Gruntfile.coffee
index f5abaf9..103e92f 100644
--- a/Gruntfile.coffee
+++ b/Gruntfile.coffee
@@ -223,4 +223,4 @@ module.exports = (grunt) ->
     grunt.registerTask 'build', ['concat:dist', 'sass']
     grunt.registerTask 'minify', ['cssmin', 'uglify']
     grunt.registerTask 'default', ['lint', 'build', 'test', 'minify']
-    grunt.registerTask 'build_modules', ['concat:axis', 'concat:chart', 'concat:chartinternal']
+    # grunt.registerTask 'build_modules', ['concat:axis', 'concat:chart', 'concat:chartinternal']
diff --git a/c3.js b/c3.js
index 06e7792..1c02c57 100644
--- a/c3.js
+++ b/c3.js
@@ -4,105 +4,23 @@
   (factory((global.c3 = global.c3 || {}),global.d3));
 }(this, (function (exports,d3) { 'use strict';
 
-var _typeof = typeof Symbol === "function" && typeof Symbol.iterator === "symbol" ? function (obj) {
-  return typeof obj;
-} : function (obj) {
-  return obj && typeof Symbol === "function" && obj.constructor === Symbol ? "symbol" : typeof obj;
-};
-
-
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-var set = function set(object, property, value, receiver) {
-  var desc = Object.getOwnPropertyDescriptor(object, property);
-
-  if (desc === undefined) {
-    var parent = Object.getPrototypeOf(object);
-
-    if (parent !== null) {
-      set(parent, property, value, receiver);
-    }
-  } else if ("value" in desc && desc.writable) {
-    desc.value = value;
-  } else {
-    var setter = desc.set;
-
-    if (setter !== undefined) {
-      setter.call(receiver, value);
-    }
-  }
-
-  return value;
-};
-
-function API(owner) {
-    this.owner = owner;
-}
-
-function inherit(base, derived) {
-    if (Object.create) {
-        derived.prototype = Object.create(base.prototype);
-    } else {
-        var f = function f() {};
-        f.prototype = base.prototype;
-        derived.prototype = new f();
-    }
-
-    derived.prototype.constructor = derived;
-
-    return derived;
-}
-
-// Features:
-// 1. category axis
-// 2. ceil values of translate/x/y to int for half pixel antialiasing
-// 3. multiline tick text
 var tickTextCharSize = void 0;
 function c3_axis(d3$$1, params) {
-    var scale = d3$$1.scale.linear(),
-        orient = 'bottom',
-        innerTickSize = 6,
-        outerTickSize = void 0,
-        tickPadding = 3,
-        tickValues = null,
-        tickFormat = void 0,
-        tickArguments = void 0;
-
-    var tickOffset = 0,
-        tickCulling = true,
-        tickCentered = void 0;
+    var scale = d3$$1.scale.linear();
+    var orient = 'bottom';
+    var innerTickSize = 6;
+    var tickPadding = 3;
+    var tickValues = null;
+    var tickFormat = void 0;
+    var tickArguments = void 0;
+
+    var tickOffset = 0;
+    var tickCulling = true;
+    var tickCentered = void 0;
 
     params = params || {};
-    outerTickSize = params.withOuterTick ? 6 : 0;
+
+    var outerTickSize = params.withOuterTick ? 6 : 0;
 
     function axisX(selection, x) {
         selection.attr('transform', function (d) {
@@ -115,18 +33,18 @@ function c3_axis(d3$$1, params) {
         });
     }
     function scaleExtent(domain) {
-        var start = domain[0],
-            stop = domain[domain.length - 1];
+        var start = domain[0];
+        var stop = domain[domain.length - 1];
         return start < stop ? [start, stop] : [stop, start];
     }
     function generateTicks(scale) {
-        var i = void 0,
-            domain = void 0,
-            ticks = [];
+        // eslint-disable-line no-shadow
+        var i = void 0;
+        var ticks = [];
         if (scale.ticks) {
             return scale.ticks.apply(scale, tickArguments);
         }
-        domain = scale.domain();
+        var domain = scale.domain();
         for (i = Math.ceil(domain[0]); i < domain[1]; i++) {
             ticks.push(i);
         }
@@ -136,8 +54,8 @@ function c3_axis(d3$$1, params) {
         return ticks;
     }
     function copyScale() {
-        var newScale = scale.copy(),
-            domain = void 0;
+        var newScale = scale.copy();
+        var domain = void 0;
         if (params.isCategory) {
             domain = scale.domain();
             newScale.domain([domain[0], domain[1] - 1]);
@@ -179,11 +97,12 @@ function c3_axis(d3$$1, params) {
             var scale0 = this.__chart__ || scale,
                 scale1 = this.__chart__ = copyScale();
 
-            var ticks = tickValues ? tickValues : generateTicks(scale1),
+            var ticks = tickValues || generateTicks(scale1),
                 tick = g.selectAll('.tick').data(ticks, scale1),
                 tickEnter = tick.enter().insert('g', '.domain').attr('class', 'tick').style('opacity', 1e-6),
 
-            // MEMO: No exit transition. The reason is this transition affects max tick width calculation because old tick will be included in the ticks.
+            // MEMO: No exit transition. The reason is this transition affects max tick width
+            // calculation because old tick will be included in the ticks.
             tickExit = tick.exit().remove(),
                 tickUpdate = transitionise(tick).style('opacity', 1),
                 tickTransform = void 0,
@@ -213,6 +132,7 @@ function c3_axis(d3$$1, params) {
                 tspan = void 0,
                 sizeFor1Char = getSizeFor1Char(g.select('.tick')),
                 counts = [];
+
             var tickLength = Math.max(innerTickSize, 0) + tickPadding,
                 isVertical = orient === 'left' || orient === 'right';
 
@@ -242,7 +162,7 @@ function c3_axis(d3$$1, params) {
                         textWidth = sizeFor1Char.w * subtext.length;
                         // if text width gets over tick width, split by space index or crrent index
                         if (maxWidth < textWidth) {
-                            return split(splitted.concat(text.substr(0, spaceIndex ? spaceIndex : i)), text.slice(spaceIndex ? spaceIndex + 1 : i));
+                            return split(splitted.concat(text.substr(0, spaceIndex || i)), text.slice(spaceIndex ? spaceIndex + 1 : i));
                         }
                     }
                     return splitted.concat(text);
@@ -358,6 +278,8 @@ function c3_axis(d3$$1, params) {
                         pathUpdate.attr('d', 'M' + outerTickSize + ',' + range[0] + 'H0V' + range[1] + 'H' + outerTickSize);
                         break;
                     }
+                default:
+                    break;
             }
             if (scale1.rangeBand) {
                 (function () {
@@ -419,10 +341,14 @@ function c3_axis(d3$$1, params) {
         return interval === Infinity ? 0 : interval;
     };
     axis.ticks = function () {
+        for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) {
+            args[_key] = arguments[_key];
+        }
+
         if (!arguments.length) {
             return tickArguments;
         }
-        tickArguments = arguments;
+        tickArguments = args;
         return axis;
     };
     axis.tickCulling = function (culling) {
@@ -448,16 +374,76 @@ function c3_axis(d3$$1, params) {
     return axis;
 }
 
-function Axis(owner) {
+var _typeof = typeof Symbol === "function" && typeof Symbol.iterator === "symbol" ? function (obj) {
+  return typeof obj;
+} : function (obj) {
+  return obj && typeof Symbol === "function" && obj.constructor === Symbol ? "symbol" : typeof obj;
+};
+
+
+
+
+
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+
+
+
+
+
+
+
+
+
+
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+
+
+
+
+
+
+
+
+var set = function set(object, property, value, receiver) {
+  var desc = Object.getOwnPropertyDescriptor(object, property);
+
+  if (desc === undefined) {
+    var parent = Object.getPrototypeOf(object);
+
+    if (parent !== null) {
+      set(parent, property, value, receiver);
+    }
+  } else if ("value" in desc && desc.writable) {
+    desc.value = value;
+  } else {
+    var setter = desc.set;
+
+    if (setter !== undefined) {
+      setter.call(receiver, value);
+    }
+  }
+
+  return value;
+};
+
+function Axis$$1(owner) {
     API.call(this, owner);
 }
 
-inherit(API, Axis);
+inherit(API, Axis$$1);
 
-Axis.prototype.init = function init() {
-    var $$ = this.owner,
-        config = $$.config,
-        main = $$.main;
+Axis$$1.prototype.init = function init() {
+    var $$ = this.owner;
+    var config = $$.config;
+    var main = $$.main;
     $$.axes.x = main.append('g').attr('class', CLASS.axis + ' ' + CLASS.axisX).attr('clip-path', $$.clipPathForXAxis).attr('transform', $$.getTranslate('x')).style('visibility', config.axis_x_show ? 'visible' : 'hidden');
     $$.axes.x.append('text').attr('class', CLASS.axisXLabel).attr('transform', config.axis_rotated ? 'rotate(-90)' : '').style('text-anchor', this.textAnchorForXAxisLabel.bind(this));
     $$.axes.y = main.append('g').attr('class', CLASS.axis + ' ' + CLASS.axisY).attr('clip-path', config.axis_y_inner ? '' : $$.clipPathForYAxis).attr('transform', $$.getTranslate('y')).style('visibility', config.axis_y_show ? 'visible' : 'hidden');
@@ -468,18 +454,18 @@ Axis.prototype.init = function init() {
     .attr('transform', $$.getTranslate('y2')).style('visibility', config.axis_y2_show ? 'visible' : 'hidden');
     $$.axes.y2.append('text').attr('class', CLASS.axisY2Label).attr('transform', config.axis_rotated ? '' : 'rotate(-90)').style('text-anchor', this.textAnchorForY2AxisLabel.bind(this));
 };
-Axis.prototype.getXAxis = function getXAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
-    var $$ = this.owner,
-        config = $$.config,
-        axisParams = {
+Axis$$1.prototype.getXAxis = function getXAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
+    var $$ = this.owner;
+    var config = $$.config;
+    var axisParams = {
         isCategory: $$.isCategorized(),
         withOuterTick: withOuterTick,
         tickMultiline: config.axis_x_tick_multiline,
         tickWidth: config.axis_x_tick_width,
         tickTextRotate: withoutRotateTickText ? 0 : config.axis_x_tick_rotate,
         withoutTransition: withoutTransition
-    },
-        axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient);
+    };
+    var axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient);
 
     if ($$.isTimeSeries() && tickValues && typeof tickValues !== 'function') {
         tickValues = tickValues.map(function (v) {
@@ -498,10 +484,10 @@ Axis.prototype.getXAxis = function getXAxis(scale, orient, tickFormat, tickValue
 
     return axis;
 };
-Axis.prototype.updateXAxisTickValues = function updateXAxisTickValues(targets, axis) {
-    var $$ = this.owner,
-        config = $$.config,
-        tickValues = void 0;
+Axis$$1.prototype.updateXAxisTickValues = function updateXAxisTickValues(targets, axis) {
+    var $$ = this.owner;
+    var config = $$.config;
+    var tickValues = void 0;
     if (config.axis_x_tick_fit || config.axis_x_tick_count) {
         tickValues = this.generateTickValues($$.mapTargetsToUniqueXs(targets), config.axis_x_tick_count, $$.isTimeSeries());
     }
@@ -513,15 +499,15 @@ Axis.prototype.updateXAxisTickValues = function updateXAxisTickValues(targets, a
     }
     return tickValues;
 };
-Axis.prototype.getYAxis = function getYAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
-    var $$ = this.owner,
-        config = $$.config,
-        axisParams = {
+Axis$$1.prototype.getYAxis = function getYAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
+    var $$ = this.owner;
+    var config = $$.config;
+    var axisParams = {
         withOuterTick: withOuterTick,
         withoutTransition: withoutTransition,
         tickTextRotate: withoutRotateTickText ? 0 : config.axis_y_tick_rotate
-    },
-        axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient).tickFormat(tickFormat);
+    };
+    var axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient).tickFormat(tickFormat);
     if ($$.isTimeSeriesY()) {
         axis.ticks($$.d3.time[config.axis_y_tick_time_value], config.axis_y_tick_time_interval);
     } else {
@@ -529,14 +515,15 @@ Axis.prototype.getYAxis = function getYAxis(scale, orient, tickFormat, tickValue
     }
     return axis;
 };
-Axis.prototype.getId = function getId(id) {
+Axis$$1.prototype.getId = function getId(id) {
     var config = this.owner.config;
     return id in config.data_axes ? config.data_axes[id] : 'y';
 };
-Axis.prototype.getXAxisTickFormat = function getXAxisTickFormat() {
-    var $$ = this.owner,
-        config = $$.config,
-        format = $$.isTimeSeries() ? $$.defaultAxisTimeFormat : $$.isCategorized() ? $$.categoryName : function (v) {
+Axis$$1.prototype.getXAxisTickFormat = function getXAxisTickFormat() {
+    var $$ = this.owner;
+    var config = $$.config;
+    var format = $$.isTimeSeries() ? // eslint-disable-line no-nested-ternary
+    $$.defaultAxisTimeFormat : $$.isCategorized() ? $$.categoryName : function (v) {
         return v < 0 ? v.toFixed(0) : v;
     };
     if (config.axis_x_tick_format) {
@@ -552,22 +539,23 @@ Axis.prototype.getXAxisTickFormat = function getXAxisTickFormat() {
         return format.call($$, v);
     } : format;
 };
-Axis.prototype.getTickValues = function getTickValues(tickValues, axis) {
-    return tickValues ? tickValues : axis ? axis.tickValues() : undefined;
+Axis$$1.prototype.getTickValues = function getTickValues(tickValues, axis) {
+    return tickValues ? tickValues : // eslint-disable-line no-nested-ternary,no-unneeded-ternary
+    axis ? axis.tickValues() : undefined;
 };
-Axis.prototype.getXAxisTickValues = function getXAxisTickValues() {
+Axis$$1.prototype.getXAxisTickValues = function getXAxisTickValues() {
     return this.getTickValues(this.owner.config.axis_x_tick_values, this.owner.xAxis);
 };
-Axis.prototype.getYAxisTickValues = function getYAxisTickValues() {
+Axis$$1.prototype.getYAxisTickValues = function getYAxisTickValues() {
     return this.getTickValues(this.owner.config.axis_y_tick_values, this.owner.yAxis);
 };
-Axis.prototype.getY2AxisTickValues = function getY2AxisTickValues() {
+Axis$$1.prototype.getY2AxisTickValues = function getY2AxisTickValues() {
     return this.getTickValues(this.owner.config.axis_y2_tick_values, this.owner.y2Axis);
 };
-Axis.prototype.getLabelOptionByAxisId = function getLabelOptionByAxisId(axisId) {
-    var $$ = this.owner,
-        config = $$.config,
-        option = void 0;
+Axis$$1.prototype.getLabelOptionByAxisId = function getLabelOptionByAxisId(axisId) {
+    var $$ = this.owner;
+    var config = $$.config;
+    var option = void 0;
     if (axisId === 'y') {
         option = config.axis_y_label;
     } else if (axisId === 'y2') {
@@ -577,14 +565,14 @@ Axis.prototype.getLabelOptionByAxisId = function getLabelOptionByAxisId(axisId)
     }
     return option;
 };
-Axis.prototype.getLabelText = function getLabelText(axisId) {
+Axis$$1.prototype.getLabelText = function getLabelText(axisId) {
     var option = this.getLabelOptionByAxisId(axisId);
-    return isString(option) ? option : option ? option.text : null;
+    return isString(option) ? option : option ? option.text : null; // eslint-disable-line no-nested-ternary,max-len
 };
-Axis.prototype.setLabelText = function setLabelText(axisId, text) {
-    var $$ = this.owner,
-        config = $$.config,
-        option = this.getLabelOptionByAxisId(axisId);
+Axis$$1.prototype.setLabelText = function setLabelText(axisId, text) {
+    var $$ = this.owner;
+    var config = $$.config;
+    var option = this.getLabelOptionByAxisId(axisId);
     if (isString(option)) {
         if (axisId === 'y') {
             config.axis_y_label = text;
@@ -597,9 +585,9 @@ Axis.prototype.setLabelText = function setLabelText(axisId, text) {
         option.text = text;
     }
 };
-Axis.prototype.getLabelPosition = function getLabelPosition(axisId, defaultPosition) {
-    var option = this.getLabelOptionByAxisId(axisId),
-        position = option && (typeof option === 'undefined' ? 'undefined' : _typeof(option)) === 'object' && option.position ? option.position : defaultPosition;
+Axis$$1.prototype.getLabelPosition = function getLabelPosition(axisId, defaultPosition) {
+    var option = this.getLabelOptionByAxisId(axisId);
+    var position = option && (typeof option === 'undefined' ? 'undefined' : _typeof(option)) === 'object' && option.position ? option.position : defaultPosition;
     return {
         isInner: position.indexOf('inner') >= 0,
         isOuter: position.indexOf('outer') >= 0,
@@ -611,28 +599,28 @@ Axis.prototype.getLabelPosition = function getLabelPosition(axisId, defaultPosit
         isBottom: position.indexOf('bottom') >= 0
     };
 };
-Axis.prototype.getXAxisLabelPosition = function getXAxisLabelPosition() {
+Axis$$1.prototype.getXAxisLabelPosition = function getXAxisLabelPosition() {
     return this.getLabelPosition('x', this.owner.config.axis_rotated ? 'inner-top' : 'inner-right');
 };
-Axis.prototype.getYAxisLabelPosition = function getYAxisLabelPosition() {
+Axis$$1.prototype.getYAxisLabelPosition = function getYAxisLabelPosition() {
     return this.getLabelPosition('y', this.owner.config.axis_rotated ? 'inner-right' : 'inner-top');
 };
-Axis.prototype.getY2AxisLabelPosition = function getY2AxisLabelPosition() {
+Axis$$1.prototype.getY2AxisLabelPosition = function getY2AxisLabelPosition() {
     return this.getLabelPosition('y2', this.owner.config.axis_rotated ? 'inner-right' : 'inner-top');
 };
-Axis.prototype.getLabelPositionById = function getLabelPositionById(id) {
+Axis$$1.prototype.getLabelPositionById = function getLabelPositionById(id) {
     return id === 'y2' ? this.getY2AxisLabelPosition() : id === 'y' ? this.getYAxisLabelPosition() : this.getXAxisLabelPosition();
 };
-Axis.prototype.textForXAxisLabel = function textForXAxisLabel() {
+Axis$$1.prototype.textForXAxisLabel = function textForXAxisLabel() {
     return this.getLabelText('x');
 };
-Axis.prototype.textForYAxisLabel = function textForYAxisLabel() {
+Axis$$1.prototype.textForYAxisLabel = function textForYAxisLabel() {
     return this.getLabelText('y');
 };
-Axis.prototype.textForY2AxisLabel = function textForY2AxisLabel() {
+Axis$$1.prototype.textForY2AxisLabel = function textForY2AxisLabel() {
     return this.getLabelText('y2');
 };
-Axis.prototype.xForAxisLabel = function xForAxisLabel(forHorizontal, position) {
+Axis$$1.prototype.xForAxisLabel = function xForAxisLabel(forHorizontal, position) {
     var $$ = this.owner;
     if (forHorizontal) {
         return position.isLeft ? 0 : position.isCenter ? $$.width / 2 : $$.width;
@@ -640,87 +628,87 @@ Axis.prototype.xForAxisLabel = function xForAxisLabel(forHorizontal, position) {
         return position.isBottom ? -$$.height : position.isMiddle ? -$$.height / 2 : 0;
     }
 };
-Axis.prototype.dxForAxisLabel = function dxForAxisLabel(forHorizontal, position) {
+Axis$$1.prototype.dxForAxisLabel = function dxForAxisLabel(forHorizontal, position) {
     if (forHorizontal) {
         return position.isLeft ? '0.5em' : position.isRight ? '-0.5em' : '0';
     } else {
         return position.isTop ? '-0.5em' : position.isBottom ? '0.5em' : '0';
     }
 };
-Axis.prototype.textAnchorForAxisLabel = function textAnchorForAxisLabel(forHorizontal, position) {
+Axis$$1.prototype.textAnchorForAxisLabel = function textAnchorForAxisLabel(forHorizontal, position) {
     if (forHorizontal) {
         return position.isLeft ? 'start' : position.isCenter ? 'middle' : 'end';
     } else {
         return position.isBottom ? 'start' : position.isMiddle ? 'middle' : 'end';
     }
 };
-Axis.prototype.xForXAxisLabel = function xForXAxisLabel() {
+Axis$$1.prototype.xForXAxisLabel = function xForXAxisLabel() {
     return this.xForAxisLabel(!this.owner.config.axis_rotated, this.getXAxisLabelPosition());
 };
-Axis.prototype.xForYAxisLabel = function xForYAxisLabel() {
+Axis$$1.prototype.xForYAxisLabel = function xForYAxisLabel() {
     return this.xForAxisLabel(this.owner.config.axis_rotated, this.getYAxisLabelPosition());
 };
-Axis.prototype.xForY2AxisLabel = function xForY2AxisLabel() {
+Axis$$1.prototype.xForY2AxisLabel = function xForY2AxisLabel() {
     return this.xForAxisLabel(this.owner.config.axis_rotated, this.getY2AxisLabelPosition());
 };
-Axis.prototype.dxForXAxisLabel = function dxForXAxisLabel() {
+Axis$$1.prototype.dxForXAxisLabel = function dxForXAxisLabel() {
     return this.dxForAxisLabel(!this.owner.config.axis_rotated, this.getXAxisLabelPosition());
 };
-Axis.prototype.dxForYAxisLabel = function dxForYAxisLabel() {
+Axis$$1.prototype.dxForYAxisLabel = function dxForYAxisLabel() {
     return this.dxForAxisLabel(this.owner.config.axis_rotated, this.getYAxisLabelPosition());
 };
-Axis.prototype.dxForY2AxisLabel = function dxForY2AxisLabel() {
+Axis$$1.prototype.dxForY2AxisLabel = function dxForY2AxisLabel() {
     return this.dxForAxisLabel(this.owner.config.axis_rotated, this.getY2AxisLabelPosition());
 };
-Axis.prototype.dyForXAxisLabel = function dyForXAxisLabel() {
-    var $$ = this.owner,
-        config = $$.config,
-        position = this.getXAxisLabelPosition();
+Axis$$1.prototype.dyForXAxisLabel = function dyForXAxisLabel() {
+    var $$ = this.owner;
+    var config = $$.config;
+    var position = this.getXAxisLabelPosition();
     if (config.axis_rotated) {
         return position.isInner ? '1.2em' : -25 - this.getMaxTickWidth('x');
     } else {
         return position.isInner ? '-0.5em' : config.axis_x_height ? config.axis_x_height - 10 : '3em';
     }
 };
-Axis.prototype.dyForYAxisLabel = function dyForYAxisLabel() {
-    var $$ = this.owner,
-        position = this.getYAxisLabelPosition();
+Axis$$1.prototype.dyForYAxisLabel = function dyForYAxisLabel() {
+    var $$ = this.owner;
+    var position = this.getYAxisLabelPosition();
     if ($$.config.axis_rotated) {
         return position.isInner ? '-0.5em' : '3em';
     } else {
         return position.isInner ? '1.2em' : -10 - ($$.config.axis_y_inner ? 0 : this.getMaxTickWidth('y') + 10);
     }
 };
-Axis.prototype.dyForY2AxisLabel = function dyForY2AxisLabel() {
-    var $$ = this.owner,
-        position = this.getY2AxisLabelPosition();
+Axis$$1.prototype.dyForY2AxisLabel = function dyForY2AxisLabel() {
+    var $$ = this.owner;
+    var position = this.getY2AxisLabelPosition();
     if ($$.config.axis_rotated) {
         return position.isInner ? '1.2em' : '-2.2em';
     } else {
         return position.isInner ? '-0.5em' : 15 + ($$.config.axis_y2_inner ? 0 : this.getMaxTickWidth('y2') + 15);
     }
 };
-Axis.prototype.textAnchorForXAxisLabel = function textAnchorForXAxisLabel() {
+Axis$$1.prototype.textAnchorForXAxisLabel = function textAnchorForXAxisLabel() {
     var $$ = this.owner;
     return this.textAnchorForAxisLabel(!$$.config.axis_rotated, this.getXAxisLabelPosition());
 };
-Axis.prototype.textAnchorForYAxisLabel = function textAnchorForYAxisLabel() {
+Axis$$1.prototype.textAnchorForYAxisLabel = function textAnchorForYAxisLabel() {
     var $$ = this.owner;
     return this.textAnchorForAxisLabel($$.config.axis_rotated, this.getYAxisLabelPosition());
 };
-Axis.prototype.textAnchorForY2AxisLabel = function textAnchorForY2AxisLabel() {
+Axis$$1.prototype.textAnchorForY2AxisLabel = function textAnchorForY2AxisLabel() {
     var $$ = this.owner;
     return this.textAnchorForAxisLabel($$.config.axis_rotated, this.getY2AxisLabelPosition());
 };
-Axis.prototype.getMaxTickWidth = function getMaxTickWidth(id, withoutRecompute) {
-    var $$ = this.owner,
-        config = $$.config,
-        maxWidth = 0,
-        targetsToShow = void 0,
-        scale = void 0,
-        axis = void 0,
-        dummy = void 0,
-        svg = void 0;
+Axis$$1.prototype.getMaxTickWidth = function getMaxTickWidth(id, withoutRecompute) {
+    var $$ = this.owner;
+    var config = $$.config;
+    var maxWidth = 0;
+    var targetsToShow = void 0;
+    var scale = void 0;
+    var axis = void 0;
+    var dummy = void 0;
+    var svg = void 0;
     if (withoutRecompute && $$.currentMaxTickWidths[id]) {
         return $$.currentMaxTickWidths[id];
     }
@@ -738,7 +726,8 @@ Axis.prototype.getMaxTickWidth = function getMaxTickWidth(id, withoutRecompute)
             this.updateXAxisTickValues(targetsToShow, axis);
         }
         dummy = $$.d3.select('body').append('div').classed('c3', true);
-        svg = dummy.append('svg').style('visibility', 'hidden').style('position', 'fixed').style('top', 0).style('left', 0), svg.append('g').call(axis).each(function () {
+        svg = dummy.append('svg').style('visibility', 'hidden').style('position', 'fixed').style('top', 0).style('left', 0);
+        svg.append('g').call(axis).each(function () {
             $$.d3.select(this).selectAll('text').each(function () {
                 var box = this.getBoundingClientRect();
                 if (maxWidth < box.width) {
@@ -752,16 +741,16 @@ Axis.prototype.getMaxTickWidth = function getMaxTickWidth(id, withoutRecompute)
     return $$.currentMaxTickWidths[id];
 };
 
-Axis.prototype.updateLabels = function updateLabels(withTransition) {
+Axis$$1.prototype.updateLabels = function updateLabels(withTransition) {
     var $$ = this.owner;
-    var axisXLabel = $$.main.select('.' + CLASS.axisX + ' .' + CLASS.axisXLabel),
-        axisYLabel = $$.main.select('.' + CLASS.axisY + ' .' + CLASS.axisYLabel),
-        axisY2Label = $$.main.select('.' + CLASS.axisY2 + ' .' + CLASS.axisY2Label);
+    var axisXLabel = $$.main.select('.' + CLASS.axisX + ' .' + CLASS.axisXLabel);
+    var axisYLabel = $$.main.select('.' + CLASS.axisY + ' .' + CLASS.axisYLabel);
+    var axisY2Label = $$.main.select('.' + CLASS.axisY2 + ' .' + CLASS.axisY2Label);
     (withTransition ? axisXLabel.transition() : axisXLabel).attr('x', this.xForXAxisLabel.bind(this)).attr('dx', this.dxForXAxisLabel.bind(this)).attr('dy', this.dyForXAxisLabel.bind(this)).text(this.textForXAxisLabel.bind(this));
     (withTransition ? axisYLabel.transition() : axisYLabel).attr('x', this.xForYAxisLabel.bind(this)).attr('dx', this.dxForYAxisLabel.bind(this)).attr('dy', this.dyForYAxisLabel.bind(this)).text(this.textForYAxisLabel.bind(this));
     (withTransition ? axisY2Label.transition() : axisY2Label).attr('x', this.xForY2AxisLabel.bind(this)).attr('dx', this.dxForY2AxisLabel.bind(this)).attr('dy', this.dyForY2AxisLabel.bind(this)).text(this.textForY2AxisLabel.bind(this));
 };
-Axis.prototype.getPadding = function getPadding(padding, key, defaultValue, domainLength) {
+Axis$$1.prototype.getPadding = function getPadding(padding, key, defaultValue, domainLength) {
     var p = typeof padding === 'number' ? padding : padding[key];
     if (!isValue(p)) {
         return defaultValue;
@@ -772,20 +761,21 @@ Axis.prototype.getPadding = function getPadding(padding, key, defaultValue, doma
     // assume padding is pixels if unit is not specified
     return this.convertPixelsToAxisPadding(p, domainLength);
 };
-Axis.prototype.convertPixelsToAxisPadding = function convertPixelsToAxisPadding(pixels, domainLength) {
-    var $$ = this.owner,
-        length = $$.config.axis_rotated ? $$.width : $$.height;
+Axis$$1.prototype.convertPixelsToAxisPadding = function convertPixelsToAxisPadding(pixels, domainLength) {
+    // eslint-disable-line max-len
+    var $$ = this.owner;
+    var length = $$.config.axis_rotated ? $$.width : $$.height;
     return domainLength * (pixels / length);
 };
-Axis.prototype.generateTickValues = function generateTickValues(values, tickCount, forTimeSeries) {
-    var tickValues = values,
-        targetCount = void 0,
-        start = void 0,
-        end = void 0,
-        count = void 0,
-        interval = void 0,
-        i = void 0,
-        tickValue = void 0;
+Axis$$1.prototype.generateTickValues = function generateTickValues(values, tickCount, forTimeSeries) {
+    var tickValues = values;
+    var targetCount = void 0;
+    var start = void 0;
+    var end = void 0;
+    var count = void 0;
+    var interval = void 0;
+    var i = void 0;
+    var tickValue = void 0;
     if (tickCount) {
         targetCount = isFunction(tickCount) ? tickCount() : tickCount;
         // compute ticks according to tickCount
@@ -814,9 +804,9 @@ Axis.prototype.generateTickValues = function generateTickValues(values, tickCoun
     }
     return tickValues;
 };
-Axis.prototype.generateTransitions = function generateTransitions(duration) {
-    var $$ = this.owner,
-        axes = $$.axes;
+Axis$$1.prototype.generateTransitions = function generateTransitions(duration) {
+    var $$ = this.owner;
+    var axes = $$.axes;
     return {
         axisX: duration ? axes.x.transition().duration(duration) : axes.x,
         axisY: duration ? axes.y.transition().duration(duration) : axes.y,
@@ -824,7 +814,7 @@ Axis.prototype.generateTransitions = function generateTransitions(duration) {
         axisSubX: duration ? axes.subx.transition().duration(duration) : axes.subx
     };
 };
-Axis.prototype.redraw = function redraw(transitions, isHidden) {
+Axis$$1.prototype.redraw = function redraw(transitions, isHidden) {
     var $$ = this.owner;
     $$.axes.x.style('opacity', isHidden ? 0 : 1);
     $$.axes.y.style('opacity', isHidden ? 0 : 1);
@@ -836,11 +826,48 @@ Axis.prototype.redraw = function redraw(transitions, isHidden) {
     transitions.axisSubX.call($$.subXAxis);
 };
 
+// import {
+//     CLASS,
+//     isValue,
+//     isFunction,
+//     isString,
+//     isUndefined,
+//     isDefined,
+//     ceil10,
+//     asHalfPixel,
+//     diffDomain,
+//     isEmpty,
+//     notEmpty,
+//     getOption,
+//     hasValue,
+//     sanitise,
+//     getPathBox,
+//     ChartInternal } from '../chartinternal';
+
+function API(owner) {
+    this.owner = owner;
+}
+
+/* eslint-disable */
+function inherit(base, derived) {
+    if (Object.create) {
+        derived.prototype = Object.create(base.prototype);
+    } else {
+        var f = function f() {};
+        f.prototype = base.prototype;
+        derived.prototype = new f();
+    }
+
+    derived.prototype.constructor = derived;
+
+    return derived;
+}
+
 function ChartInternal(api){var $$=this;$$.d3=window.d3?window.d3:typeof require!=='undefined'?require('d3'):undefined;$$.api=api;$$.config=$$.getDefaultConfig();$$.data={};$$.cache={};$$.axes={};}var c3_chart_internal_fn=ChartInternal.prototype;c3_chart_internal_fn.beforeInit=function(){// can do something
 };c3_chart_internal_fn.afterInit=function(){// can do something
 };c3_chart_internal_fn.init=function(){var $$=this,config=$$.config;$$.initParams();if(config.data_url){$$.convertUrlToData(config.data_url,config.data_mimeType,config.data_headers,config.data_keys,$$.initWithData);}else if(config.data_json){$$.initWithData($$.convertJsonToData(config.data_json,config.data_keys));}else if(config.data_rows){$$.initWithData($$.convertRowsToData(config.data_rows));}else if(config.data_columns){$$.initWithData($$.convertColumnsToData(config.data_columns));}else{throw Error('url or json or rows or columns is required.');}};c3_chart_internal_fn.initParams=function(){var $$=this,d3$$1=$$.d3,config=$$.config;// MEMO: clipId needs to be unique because it conflicts when multiple charts exist
 $$.clipId='c3-'+ +new Date()+'-clip',$$.clipIdForXAxis=$$.clipId+'-xaxis',$$.clipIdForYAxis=$$.clipId+'-yaxis',$$.clipIdForGrid=$$.clipId+'-grid',$$.clipIdForSubchart=$$.clipId+'-subchart',$$.clipPath=$$.getClipPath($$.clipId),$$.clipPathForXAxis=$$.getClipPath($$.clipIdForXAxis),$$.clipPathForYAxis=$$.getClipPath($$.clipIdForYAxis);$$.clipPathForGrid=$$.getClipPath($$.clipIdForGrid),$$.clipPathForSubchart=$$.getClipPath($$.clipIdForSubchart),$$.dragStart=null;$$.dragging=false;$$.flowing=false;$$.cancelClick=false;$$.mouseover=false;$$.transiting=false;$$.color=$$.generateColor();$$.levelColor=$$.generateLevelColor();$$.dataTimeFormat=config.data_xLocaltime?d3$$1.time.format:d3$$1.time.format.utc;$$.axisTimeFormat=config.axis_x_localtime?d3$$1.time.format:d3$$1.time.format.utc;$$.defaultAxisTimeFormat=$$.axisTimeFormat.multi([['.%L',function(d){return d.getMilliseconds();}],[':%S',function(d){return d.getSeconds();}],['%I:%M',function(d){return d.getMinutes();}],['%I %p',function(d){return d.getHours();}],['%-m/%-d',function(d){return d.getDay()&&d.getDate()!==1;}],['%-m/%-d',function(d){return d.getDate()!==1;}],['%-m/%-d',function(d){return d.getMonth();}],['%Y/%-m/%-d',function(){return true;}]]);$$.hiddenTargetIds=[];$$.hiddenLegendIds=[];$$.focusedTargetIds=[];$$.defocusedTargetIds=[];$$.xOrient=config.axis_rotated?'left':'bottom';$$.yOrient=config.axis_rotated?config.axis_y_inner?'top':'bottom':config.axis_y_inner?'right':'left';$$.y2Orient=config.axis_rotated?config.axis_y2_inner?'bottom':'top':config.axis_y2_inner?'left':'right';$$.subXOrient=config.axis_rotated?'left':'bottom';$$.isLegendRight=config.legend_position==='right';$$.isLegendInset=config.legend_position==='inset';$$.isLegendTop=config.legend_inset_anchor==='top-left'||config.legend_inset_anchor==='top-right';$$.isLegendLeft=config.legend_inset_anchor==='top-left'||config.legend_inset_anchor==='bottom-left';$$.legendStep=0;$$.legendItemWidth=0;$$.legendItemHeight=0;$$.currentMaxTickWidths={x:0,y:0,y2:0};$$.rotated_padding_left=30;$$.rotated_padding_right=config.axis_rotated&&!config.axis_x_show?0:30;$$.rotated_padding_top=5;$$.withoutFadeIn={};$$.intervalForObserveInserted=undefined;$$.axes.subx=d3$$1.selectAll([]);// needs when excluding subchart.js
-};c3_chart_internal_fn.initChartElements=function(){if(this.initBar){this.initBar();}if(this.initLine){this.initLine();}if(this.initArc){this.initArc();}if(this.initGauge){this.initGauge();}if(this.initText){this.initText();}};c3_chart_internal_fn.initWithData=function(data){var $$=this,d3$$1=$$.d3,config=$$.config;var defs=void 0,main=void 0,binding=true;$$.axis=new Axis($$);if($$.initPie){$$.initPie();}if($$.initBrush){$$.initBrush();}if($$.initZoom){$$.initZoom();}if(!config.bindto){$$.selectChart=d3$$1.selectAll([]);}else if(typeof config.bindto.node==='function'){$$.selectChart=config.bindto;}else{$$.selectChart=d3$$1.select(config.bindto);}if($$.selectChart.empty()){$$.selectChart=d3$$1.select(document.createElement('div')).style('opacity',0);$$.observeInserted($$.selectChart);binding=false;}$$.selectChart.html('').classed('c3',true);// Init data as targets
+};c3_chart_internal_fn.initChartElements=function(){if(this.initBar){this.initBar();}if(this.initLine){this.initLine();}if(this.initArc){this.initArc();}if(this.initGauge){this.initGauge();}if(this.initText){this.initText();}};c3_chart_internal_fn.initWithData=function(data){var $$=this,d3$$1=$$.d3,config=$$.config;var defs=void 0,main=void 0,binding=true;$$.axis=new Axis$$1($$);if($$.initPie){$$.initPie();}if($$.initBrush){$$.initBrush();}if($$.initZoom){$$.initZoom();}if(!config.bindto){$$.selectChart=d3$$1.selectAll([]);}else if(typeof config.bindto.node==='function'){$$.selectChart=config.bindto;}else{$$.selectChart=d3$$1.select(config.bindto);}if($$.selectChart.empty()){$$.selectChart=d3$$1.select(document.createElement('div')).style('opacity',0);$$.observeInserted($$.selectChart);binding=false;}$$.selectChart.html('').classed('c3',true);// Init data as targets
 $$.data.xs={};$$.data.targets=$$.convertDataToTargets(data);if(config.data_filter){$$.data.targets=$$.data.targets.filter(config.data_filter);}// Set targets to hide if needed
 if(config.data_hide){$$.addHiddenTargetIds(config.data_hide===true?$$.mapToIds($$.data.targets):config.data_hide);}if(config.legend_hide){$$.addHiddenLegendIds(config.legend_hide===true?$$.mapToIds($$.data.targets):config.legend_hide);}// when gauge, hide legend // TODO: fix
 if($$.hasType('gauge')){config.legend_show=false;}// Init sizes and scales
@@ -2030,17 +2057,24 @@ c3_chart_fn.tooltip.hide = function () {
     this.internal.config.tooltip_onhide.call(this);
 };
 
-// This file is only the entry point for rollup
-var version = "0.4.11";
+/**
+ * C3.js
+ * (c) 2016 Masayuki Tanaka and the C3.js contributors (See package.json)
+ * License: MIT
+ */
+
+var version = '0.4.11';
+
 var generate = function generate(config) {
     return new Chart(config);
 };
+
 var chart = {
     fn: Chart.prototype,
     internal: {
         fn: ChartInternal.prototype,
         axis: {
-            fn: Axis.prototype
+            fn: Axis$$1.prototype
         }
     }
 };
diff --git a/es6_modules/axis.js b/es6_modules/axis.js
deleted file mode 100644
index 3da6dc7..0000000
--- a/es6_modules/axis.js
+++ /dev/null
@@ -1,734 +0,0 @@
-import {CLASS,isValue,isFunction,isString,isUndefined,isDefined,ceil10,asHalfPixel,diffDomain,isEmpty,notEmpty,getOption,hasValue,sanitise,getPathBox, ChartInternal} from './chartinternal.js';
-function API(owner) {
-    this.owner = owner;
-}
-
-function inherit(base, derived) {
-    if (Object.create) {
-        derived.prototype = Object.create(base.prototype);
-    } else {
-        const f = function f() {};
-        f.prototype = base.prototype;
-        derived.prototype = new f();
-    }
-
-    derived.prototype.constructor = derived;
-
-    return derived;
-}
-
-// Features:
-// 1. category axis
-// 2. ceil values of translate/x/y to int for half pixel antialiasing
-// 3. multiline tick text
-let tickTextCharSize;
-function c3_axis(d3, params) {
-    let scale = d3.scale.linear(), orient = 'bottom', innerTickSize = 6, outerTickSize, tickPadding = 3, tickValues = null, tickFormat, tickArguments;
-
-    let tickOffset = 0, tickCulling = true, tickCentered;
-
-    params = params || {};
-    outerTickSize = params.withOuterTick ? 6 : 0;
-
-    function axisX(selection, x) {
-        selection.attr('transform', (d) => {
-            return 'translate(' + Math.ceil(x(d) + tickOffset) + ', 0)';
-        });
-    }
-    function axisY(selection, y) {
-        selection.attr('transform', (d) => {
-            return 'translate(0,' + Math.ceil(y(d)) + ')';
-        });
-    }
-    function scaleExtent(domain) {
-        let start = domain[0], stop = domain[domain.length - 1];
-        return start < stop ? [start, stop] : [stop, start];
-    }
-    function generateTicks(scale) {
-        let i, domain, ticks = [];
-        if (scale.ticks) {
-            return scale.ticks.apply(scale, tickArguments);
-        }
-        domain = scale.domain();
-        for (i = Math.ceil(domain[0]); i < domain[1]; i++) {
-            ticks.push(i);
-        }
-        if (ticks.length > 0 && ticks[0] > 0) {
-            ticks.unshift(ticks[0] - (ticks[1] - ticks[0]));
-        }
-        return ticks;
-    }
-    function copyScale() {
-        let newScale = scale.copy(), domain;
-        if (params.isCategory) {
-            domain = scale.domain();
-            newScale.domain([domain[0], domain[1] - 1]);
-        }
-        return newScale;
-    }
-    function textFormatted(v) {
-        const formatted = tickFormat ? tickFormat(v) : v;
-        return typeof formatted !== 'undefined' ? formatted : '';
-    }
-    function getSizeFor1Char(tick) {
-        if (tickTextCharSize) {
-            return tickTextCharSize;
-        }
-        const size = {
-            h: 11.5,
-            w: 5.5,
-        };
-        tick.select('text').text(textFormatted).each(function (d) {
-            let box = this.getBoundingClientRect(),
-                text = textFormatted(d),
-                h = box.height,
-                w = text ? (box.width / text.length) : undefined;
-            if (h && w) {
-                size.h = h;
-                size.w = w;
-            }
-        }).text('');
-        tickTextCharSize = size;
-        return size;
-    }
-    function transitionise(selection) {
-        return params.withoutTransition ? selection : d3.transition(selection);
-    }
-    function axis(g) {
-        g.each(function () {
-            const g = axis.g = d3.select(this);
-
-            let scale0 = this.__chart__ || scale, scale1 = this.__chart__ = copyScale();
-
-            let ticks = tickValues ? tickValues : generateTicks(scale1),
-                tick = g.selectAll('.tick').data(ticks, scale1),
-                tickEnter = tick.enter().insert('g', '.domain').attr('class', 'tick').style('opacity', 1e-6),
-                // MEMO: No exit transition. The reason is this transition affects max tick width calculation because old tick will be included in the ticks.
-                tickExit = tick.exit().remove(),
-                tickUpdate = transitionise(tick).style('opacity', 1),
-                tickTransform, tickX, tickY;
-
-            let range = scale.rangeExtent ? scale.rangeExtent() : scaleExtent(scale.range()),
-                path = g.selectAll('.domain').data([0]),
-                pathUpdate = (path.enter().append('path').attr('class', 'domain'), transitionise(path));
-            tickEnter.append('line');
-            tickEnter.append('text');
-
-            let lineEnter = tickEnter.select('line'),
-                lineUpdate = tickUpdate.select('line'),
-                textEnter = tickEnter.select('text'),
-                textUpdate = tickUpdate.select('text');
-
-            if (params.isCategory) {
-                tickOffset = Math.ceil((scale1(1) - scale1(0)) / 2);
-                tickX = tickCentered ? 0 : tickOffset;
-                tickY = tickCentered ? tickOffset : 0;
-            } else {
-                tickOffset = tickX = 0;
-            }
-
-            let text, tspan, sizeFor1Char = getSizeFor1Char(g.select('.tick')), counts = [];
-            let tickLength = Math.max(innerTickSize, 0) + tickPadding,
-                isVertical = orient === 'left' || orient === 'right';
-
-            // this should be called only when category axis
-            function splitTickText(d, maxWidth) {
-                let tickText = textFormatted(d),
-                    subtext, spaceIndex, textWidth, splitted = [];
-
-                if (Object.prototype.toString.call(tickText) === '[object Array]') {
-                    return tickText;
-                }
-
-                if (!maxWidth || maxWidth <= 0) {
-                    maxWidth = isVertical ? 95 : params.isCategory ? (Math.ceil(scale1(ticks[1]) - scale1(ticks[0])) - 12) : 110;
-                }
-
-                function split(splitted, text) {
-                    spaceIndex = undefined;
-                    for (let i = 1; i < text.length; i++) {
-                        if (text.charAt(i) === ' ') {
-                            spaceIndex = i;
-                        }
-                        subtext = text.substr(0, i + 1);
-                        textWidth = sizeFor1Char.w * subtext.length;
-                        // if text width gets over tick width, split by space index or crrent index
-                        if (maxWidth < textWidth) {
-                            return split(
-                                splitted.concat(text.substr(0, spaceIndex ? spaceIndex : i)),
-                                text.slice(spaceIndex ? spaceIndex + 1 : i)
-                            );
-                        }
-                    }
-                    return splitted.concat(text);
-                }
-
-                return split(splitted, tickText + '');
-            }
-
-            function tspanDy(d, i) {
-                let dy = sizeFor1Char.h;
-                if (i === 0) {
-                    if (orient === 'left' || orient === 'right') {
-                        dy = -((counts[d.index] - 1) * (sizeFor1Char.h / 2) - 3);
-                    } else {
-                        dy = '.71em';
-                    }
-                }
-                return dy;
-            }
-
-            function tickSize(d) {
-                const tickPosition = scale(d) + (tickCentered ? 0 : tickOffset);
-                return range[0] < tickPosition && tickPosition < range[1] ? innerTickSize : 0;
-            }
-
-            text = tick.select('text');
-            tspan = text.selectAll('tspan')
-                .data((d, i) => {
-                    const splitted = params.tickMultiline ? splitTickText(d, params.tickWidth) : [].concat(textFormatted(d));
-                    counts[i] = splitted.length;
-                    return splitted.map((s) => {
-                        return { index: i, splitted: s };
-                    });
-                });
-            tspan.enter().append('tspan');
-            tspan.exit().remove();
-            tspan.text((d) => { return d.splitted; });
-
-            const rotate = params.tickTextRotate;
-
-            function textAnchorForText(rotate) {
-                if (!rotate) {
-                    return 'middle';
-                }
-                return rotate > 0 ? 'start' : 'end';
-            }
-            function textTransform(rotate) {
-                if (!rotate) {
-                    return '';
-                }
-                return 'rotate(' + rotate + ')';
-            }
-            function dxForText(rotate) {
-                if (!rotate) {
-                    return 0;
-                }
-                return 8 * Math.sin(Math.PI * (rotate / 180));
-            }
-            function yForText(rotate) {
-                if (!rotate) {
-                    return tickLength;
-                }
-                return 11.5 - 2.5 * (rotate / 15) * (rotate > 0 ? 1 : -1);
-            }
-
-            switch (orient) {
-            case 'bottom':
-                {
-                    tickTransform = axisX;
-                    lineEnter.attr('y2', innerTickSize);
-                    textEnter.attr('y', tickLength);
-                    lineUpdate.attr('x1', tickX).attr('x2', tickX).attr('y2', tickSize);
-                    textUpdate.attr('x', 0).attr('y', yForText(rotate))
-                        .style('text-anchor', textAnchorForText(rotate))
-                        .attr('transform', textTransform(rotate));
-                    tspan.attr('x', 0).attr('dy', tspanDy).attr('dx', dxForText(rotate));
-                    pathUpdate.attr('d', 'M' + range[0] + ',' + outerTickSize + 'V0H' + range[1] + 'V' + outerTickSize);
-                    break;
-                }
-            case 'top':
-                {
-                    // TODO: rotated tick text
-                    tickTransform = axisX;
-                    lineEnter.attr('y2', -innerTickSize);
-                    textEnter.attr('y', -tickLength);
-                    lineUpdate.attr('x2', 0).attr('y2', -innerTickSize);
-                    textUpdate.attr('x', 0).attr('y', -tickLength);
-                    text.style('text-anchor', 'middle');
-                    tspan.attr('x', 0).attr('dy', '0em');
-                    pathUpdate.attr('d', 'M' + range[0] + ',' + -outerTickSize + 'V0H' + range[1] + 'V' + -outerTickSize);
-                    break;
-                }
-            case 'left':
-                {
-                    tickTransform = axisY;
-                    lineEnter.attr('x2', -innerTickSize);
-                    textEnter.attr('x', -tickLength);
-                    lineUpdate.attr('x2', -innerTickSize).attr('y1', tickY).attr('y2', tickY);
-                    textUpdate.attr('x', -tickLength).attr('y', tickOffset);
-                    text.style('text-anchor', 'end');
-                    tspan.attr('x', -tickLength).attr('dy', tspanDy);
-                    pathUpdate.attr('d', 'M' + -outerTickSize + ',' + range[0] + 'H0V' + range[1] + 'H' + -outerTickSize);
-                    break;
-                }
-            case 'right':
-                {
-                    tickTransform = axisY;
-                    lineEnter.attr('x2', innerTickSize);
-                    textEnter.attr('x', tickLength);
-                    lineUpdate.attr('x2', innerTickSize).attr('y2', 0);
-                    textUpdate.attr('x', tickLength).attr('y', 0);
-                    text.style('text-anchor', 'start');
-                    tspan.attr('x', tickLength).attr('dy', tspanDy);
-                    pathUpdate.attr('d', 'M' + outerTickSize + ',' + range[0] + 'H0V' + range[1] + 'H' + outerTickSize);
-                    break;
-                }
-            }
-            if (scale1.rangeBand) {
-                let x = scale1, dx = x.rangeBand() / 2;
-                scale0 = scale1 = function (d) {
-                    return x(d) + dx;
-                };
-            } else if (scale0.rangeBand) {
-                scale0 = scale1;
-            } else {
-                tickExit.call(tickTransform, scale1);
-            }
-            tickEnter.call(tickTransform, scale0);
-            tickUpdate.call(tickTransform, scale1);
-        });
-    }
-    axis.scale = function (x) {
-        if (!arguments.length) { return scale; }
-        scale = x;
-        return axis;
-    };
-    axis.orient = function (x) {
-        if (!arguments.length) { return orient; }
-        orient = x in { top: 1, right: 1, bottom: 1, left: 1 } ? x + '' : 'bottom';
-        return axis;
-    };
-    axis.tickFormat = function (format) {
-        if (!arguments.length) { return tickFormat; }
-        tickFormat = format;
-        return axis;
-    };
-    axis.tickCentered = function (isCentered) {
-        if (!arguments.length) { return tickCentered; }
-        tickCentered = isCentered;
-        return axis;
-    };
-    axis.tickOffset = function () {
-        return tickOffset;
-    };
-    axis.tickInterval = function () {
-        let interval, length;
-        if (params.isCategory) {
-            interval = tickOffset * 2;
-        }
-        else {
-            length = axis.g.select('path.domain').node().getTotalLength() - outerTickSize * 2;
-            interval = length / axis.g.selectAll('line').size();
-        }
-        return interval === Infinity ? 0 : interval;
-    };
-    axis.ticks = function () {
-        if (!arguments.length) { return tickArguments; }
-        tickArguments = arguments;
-        return axis;
-    };
-    axis.tickCulling = function (culling) {
-        if (!arguments.length) { return tickCulling; }
-        tickCulling = culling;
-        return axis;
-    };
-    axis.tickValues = function (x) {
-        if (typeof x === 'function') {
-            tickValues = function () {
-                return x(scale.domain());
-            };
-        }
-        else {
-            if (!arguments.length) { return tickValues; }
-            tickValues = x;
-        }
-        return axis;
-    };
-    return axis;
-}
-
-function Axis(owner) {
-    API.call(this, owner);
-}
-
-inherit(API, Axis);
-
-Axis.prototype.init = function init() {
-    let $$ = this.owner, config = $$.config, main = $$.main;
-    $$.axes.x = main.append('g')
-        .attr('class', CLASS.axis + ' ' + CLASS.axisX)
-        .attr('clip-path', $$.clipPathForXAxis)
-        .attr('transform', $$.getTranslate('x'))
-        .style('visibility', config.axis_x_show ? 'visible' : 'hidden');
-    $$.axes.x.append('text')
-        .attr('class', CLASS.axisXLabel)
-        .attr('transform', config.axis_rotated ? 'rotate(-90)' : '')
-        .style('text-anchor', this.textAnchorForXAxisLabel.bind(this));
-    $$.axes.y = main.append('g')
-        .attr('class', CLASS.axis + ' ' + CLASS.axisY)
-        .attr('clip-path', config.axis_y_inner ? '' : $$.clipPathForYAxis)
-        .attr('transform', $$.getTranslate('y'))
-        .style('visibility', config.axis_y_show ? 'visible' : 'hidden');
-    $$.axes.y.append('text')
-        .attr('class', CLASS.axisYLabel)
-        .attr('transform', config.axis_rotated ? '' : 'rotate(-90)')
-        .style('text-anchor', this.textAnchorForYAxisLabel.bind(this));
-
-    $$.axes.y2 = main.append('g')
-        .attr('class', CLASS.axis + ' ' + CLASS.axisY2)
-        // clip-path?
-        .attr('transform', $$.getTranslate('y2'))
-        .style('visibility', config.axis_y2_show ? 'visible' : 'hidden');
-    $$.axes.y2.append('text')
-        .attr('class', CLASS.axisY2Label)
-        .attr('transform', config.axis_rotated ? '' : 'rotate(-90)')
-        .style('text-anchor', this.textAnchorForY2AxisLabel.bind(this));
-};
-Axis.prototype.getXAxis = function getXAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
-    let $$ = this.owner, config = $$.config,
-        axisParams = {
-            isCategory: $$.isCategorized(),
-            withOuterTick,
-            tickMultiline: config.axis_x_tick_multiline,
-            tickWidth: config.axis_x_tick_width,
-            tickTextRotate: withoutRotateTickText ? 0 : config.axis_x_tick_rotate,
-            withoutTransition,
-        },
-        axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient);
-
-    if ($$.isTimeSeries() && tickValues && typeof tickValues !== 'function') {
-        tickValues = tickValues.map((v) => { return $$.parseDate(v); });
-    }
-
-    // Set tick
-    axis.tickFormat(tickFormat).tickValues(tickValues);
-    if ($$.isCategorized()) {
-        axis.tickCentered(config.axis_x_tick_centered);
-        if (isEmpty(config.axis_x_tick_culling)) {
-            config.axis_x_tick_culling = false;
-        }
-    }
-
-    return axis;
-};
-Axis.prototype.updateXAxisTickValues = function updateXAxisTickValues(targets, axis) {
-    let $$ = this.owner, config = $$.config, tickValues;
-    if (config.axis_x_tick_fit || config.axis_x_tick_count) {
-        tickValues = this.generateTickValues($$.mapTargetsToUniqueXs(targets), config.axis_x_tick_count, $$.isTimeSeries());
-    }
-    if (axis) {
-        axis.tickValues(tickValues);
-    } else {
-        $$.xAxis.tickValues(tickValues);
-        $$.subXAxis.tickValues(tickValues);
-    }
-    return tickValues;
-};
-Axis.prototype.getYAxis = function getYAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
-    let $$ = this.owner, config = $$.config,
-        axisParams = {
-            withOuterTick,
-            withoutTransition,
-            tickTextRotate: withoutRotateTickText ? 0 : config.axis_y_tick_rotate,
-        },
-        axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient).tickFormat(tickFormat);
-    if ($$.isTimeSeriesY()) {
-        axis.ticks($$.d3.time[config.axis_y_tick_time_value], config.axis_y_tick_time_interval);
-    } else {
-        axis.tickValues(tickValues);
-    }
-    return axis;
-};
-Axis.prototype.getId = function getId(id) {
-    const config = this.owner.config;
-    return id in config.data_axes ? config.data_axes[id] : 'y';
-};
-Axis.prototype.getXAxisTickFormat = function getXAxisTickFormat() {
-    let $$ = this.owner, config = $$.config,
-        format = $$.isTimeSeries() ? $$.defaultAxisTimeFormat : $$.isCategorized() ? $$.categoryName : function (v) { return v < 0 ? v.toFixed(0) : v; };
-    if (config.axis_x_tick_format) {
-        if (isFunction(config.axis_x_tick_format)) {
-            format = config.axis_x_tick_format;
-        } else if ($$.isTimeSeries()) {
-            format = function (date) {
-                return date ? $$.axisTimeFormat(config.axis_x_tick_format)(date) : '';
-            };
-        }
-    }
-    return isFunction(format) ? function (v) { return format.call($$, v); } : format;
-};
-Axis.prototype.getTickValues = function getTickValues(tickValues, axis) {
-    return tickValues ? tickValues : axis ? axis.tickValues() : undefined;
-};
-Axis.prototype.getXAxisTickValues = function getXAxisTickValues() {
-    return this.getTickValues(this.owner.config.axis_x_tick_values, this.owner.xAxis);
-};
-Axis.prototype.getYAxisTickValues = function getYAxisTickValues() {
-    return this.getTickValues(this.owner.config.axis_y_tick_values, this.owner.yAxis);
-};
-Axis.prototype.getY2AxisTickValues = function getY2AxisTickValues() {
-    return this.getTickValues(this.owner.config.axis_y2_tick_values, this.owner.y2Axis);
-};
-Axis.prototype.getLabelOptionByAxisId = function getLabelOptionByAxisId(axisId) {
-    let $$ = this.owner, config = $$.config, option;
-    if (axisId === 'y') {
-        option = config.axis_y_label;
-    } else if (axisId === 'y2') {
-        option = config.axis_y2_label;
-    } else if (axisId === 'x') {
-        option = config.axis_x_label;
-    }
-    return option;
-};
-Axis.prototype.getLabelText = function getLabelText(axisId) {
-    const option = this.getLabelOptionByAxisId(axisId);
-    return isString(option) ? option : option ? option.text : null;
-};
-Axis.prototype.setLabelText = function setLabelText(axisId, text) {
-    let $$ = this.owner, config = $$.config,
-        option = this.getLabelOptionByAxisId(axisId);
-    if (isString(option)) {
-        if (axisId === 'y') {
-            config.axis_y_label = text;
-        } else if (axisId === 'y2') {
-            config.axis_y2_label = text;
-        } else if (axisId === 'x') {
-            config.axis_x_label = text;
-        }
-    } else if (option) {
-        option.text = text;
-    }
-};
-Axis.prototype.getLabelPosition = function getLabelPosition(axisId, defaultPosition) {
-    let option = this.getLabelOptionByAxisId(axisId),
-        position = (option && typeof option === 'object' && option.position) ? option.position : defaultPosition;
-    return {
-        isInner: position.indexOf('inner') >= 0,
-        isOuter: position.indexOf('outer') >= 0,
-        isLeft: position.indexOf('left') >= 0,
-        isCenter: position.indexOf('center') >= 0,
-        isRight: position.indexOf('right') >= 0,
-        isTop: position.indexOf('top') >= 0,
-        isMiddle: position.indexOf('middle') >= 0,
-        isBottom: position.indexOf('bottom') >= 0,
-    };
-};
-Axis.prototype.getXAxisLabelPosition = function getXAxisLabelPosition() {
-    return this.getLabelPosition('x', this.owner.config.axis_rotated ? 'inner-top' : 'inner-right');
-};
-Axis.prototype.getYAxisLabelPosition = function getYAxisLabelPosition() {
-    return this.getLabelPosition('y', this.owner.config.axis_rotated ? 'inner-right' : 'inner-top');
-};
-Axis.prototype.getY2AxisLabelPosition = function getY2AxisLabelPosition() {
-    return this.getLabelPosition('y2', this.owner.config.axis_rotated ? 'inner-right' : 'inner-top');
-};
-Axis.prototype.getLabelPositionById = function getLabelPositionById(id) {
-    return id === 'y2' ? this.getY2AxisLabelPosition() : id === 'y' ? this.getYAxisLabelPosition() : this.getXAxisLabelPosition();
-};
-Axis.prototype.textForXAxisLabel = function textForXAxisLabel() {
-    return this.getLabelText('x');
-};
-Axis.prototype.textForYAxisLabel = function textForYAxisLabel() {
-    return this.getLabelText('y');
-};
-Axis.prototype.textForY2AxisLabel = function textForY2AxisLabel() {
-    return this.getLabelText('y2');
-};
-Axis.prototype.xForAxisLabel = function xForAxisLabel(forHorizontal, position) {
-    const $$ = this.owner;
-    if (forHorizontal) {
-        return position.isLeft ? 0 : position.isCenter ? $$.width / 2 : $$.width;
-    } else {
-        return position.isBottom ? -$$.height : position.isMiddle ? -$$.height / 2 : 0;
-    }
-};
-Axis.prototype.dxForAxisLabel = function dxForAxisLabel(forHorizontal, position) {
-    if (forHorizontal) {
-        return position.isLeft ? '0.5em' : position.isRight ? '-0.5em' : '0';
-    } else {
-        return position.isTop ? '-0.5em' : position.isBottom ? '0.5em' : '0';
-    }
-};
-Axis.prototype.textAnchorForAxisLabel = function textAnchorForAxisLabel(forHorizontal, position) {
-    if (forHorizontal) {
-        return position.isLeft ? 'start' : position.isCenter ? 'middle' : 'end';
-    } else {
-        return position.isBottom ? 'start' : position.isMiddle ? 'middle' : 'end';
-    }
-};
-Axis.prototype.xForXAxisLabel = function xForXAxisLabel() {
-    return this.xForAxisLabel(!this.owner.config.axis_rotated, this.getXAxisLabelPosition());
-};
-Axis.prototype.xForYAxisLabel = function xForYAxisLabel() {
-    return this.xForAxisLabel(this.owner.config.axis_rotated, this.getYAxisLabelPosition());
-};
-Axis.prototype.xForY2AxisLabel = function xForY2AxisLabel() {
-    return this.xForAxisLabel(this.owner.config.axis_rotated, this.getY2AxisLabelPosition());
-};
-Axis.prototype.dxForXAxisLabel = function dxForXAxisLabel() {
-    return this.dxForAxisLabel(!this.owner.config.axis_rotated, this.getXAxisLabelPosition());
-};
-Axis.prototype.dxForYAxisLabel = function dxForYAxisLabel() {
-    return this.dxForAxisLabel(this.owner.config.axis_rotated, this.getYAxisLabelPosition());
-};
-Axis.prototype.dxForY2AxisLabel = function dxForY2AxisLabel() {
-    return this.dxForAxisLabel(this.owner.config.axis_rotated, this.getY2AxisLabelPosition());
-};
-Axis.prototype.dyForXAxisLabel = function dyForXAxisLabel() {
-    let $$ = this.owner, config = $$.config,
-        position = this.getXAxisLabelPosition();
-    if (config.axis_rotated) {
-        return position.isInner ? '1.2em' : -25 - this.getMaxTickWidth('x');
-    } else {
-        return position.isInner ? '-0.5em' : config.axis_x_height ? config.axis_x_height - 10 : '3em';
-    }
-};
-Axis.prototype.dyForYAxisLabel = function dyForYAxisLabel() {
-    let $$ = this.owner,
-        position = this.getYAxisLabelPosition();
-    if ($$.config.axis_rotated) {
-        return position.isInner ? '-0.5em' : '3em';
-    } else {
-        return position.isInner ? '1.2em' : -10 - ($$.config.axis_y_inner ? 0 : (this.getMaxTickWidth('y') + 10));
-    }
-};
-Axis.prototype.dyForY2AxisLabel = function dyForY2AxisLabel() {
-    let $$ = this.owner,
-        position = this.getY2AxisLabelPosition();
-    if ($$.config.axis_rotated) {
-        return position.isInner ? '1.2em' : '-2.2em';
-    } else {
-        return position.isInner ? '-0.5em' : 15 + ($$.config.axis_y2_inner ? 0 : (this.getMaxTickWidth('y2') + 15));
-    }
-};
-Axis.prototype.textAnchorForXAxisLabel = function textAnchorForXAxisLabel() {
-    const $$ = this.owner;
-    return this.textAnchorForAxisLabel(!$$.config.axis_rotated, this.getXAxisLabelPosition());
-};
-Axis.prototype.textAnchorForYAxisLabel = function textAnchorForYAxisLabel() {
-    const $$ = this.owner;
-    return this.textAnchorForAxisLabel($$.config.axis_rotated, this.getYAxisLabelPosition());
-};
-Axis.prototype.textAnchorForY2AxisLabel = function textAnchorForY2AxisLabel() {
-    const $$ = this.owner;
-    return this.textAnchorForAxisLabel($$.config.axis_rotated, this.getY2AxisLabelPosition());
-};
-Axis.prototype.getMaxTickWidth = function getMaxTickWidth(id, withoutRecompute) {
-    let $$ = this.owner, config = $$.config,
-        maxWidth = 0, targetsToShow, scale, axis, dummy, svg;
-    if (withoutRecompute && $$.currentMaxTickWidths[id]) {
-        return $$.currentMaxTickWidths[id];
-    }
-    if ($$.svg) {
-        targetsToShow = $$.filterTargetsToShow($$.data.targets);
-        if (id === 'y') {
-            scale = $$.y.copy().domain($$.getYDomain(targetsToShow, 'y'));
-            axis = this.getYAxis(scale, $$.yOrient, config.axis_y_tick_format, $$.yAxisTickValues, false, true, true);
-        } else if (id === 'y2') {
-            scale = $$.y2.copy().domain($$.getYDomain(targetsToShow, 'y2'));
-            axis = this.getYAxis(scale, $$.y2Orient, config.axis_y2_tick_format, $$.y2AxisTickValues, false, true, true);
-        } else {
-            scale = $$.x.copy().domain($$.getXDomain(targetsToShow));
-            axis = this.getXAxis(scale, $$.xOrient, $$.xAxisTickFormat, $$.xAxisTickValues, false, true, true);
-            this.updateXAxisTickValues(targetsToShow, axis);
-        }
-        dummy = $$.d3.select('body').append('div').classed('c3', true);
-        svg = dummy.append('svg').style('visibility', 'hidden').style('position', 'fixed').style('top', 0).style('left', 0),
-        svg.append('g').call(axis).each(function () {
-            $$.d3.select(this).selectAll('text').each(function () {
-                const box = this.getBoundingClientRect();
-                if (maxWidth < box.width) { maxWidth = box.width; }
-            });
-            dummy.remove();
-        });
-    }
-    $$.currentMaxTickWidths[id] = maxWidth <= 0 ? $$.currentMaxTickWidths[id] : maxWidth;
-    return $$.currentMaxTickWidths[id];
-};
-
-Axis.prototype.updateLabels = function updateLabels(withTransition) {
-    const $$ = this.owner;
-    let axisXLabel = $$.main.select('.' + CLASS.axisX + ' .' + CLASS.axisXLabel),
-        axisYLabel = $$.main.select('.' + CLASS.axisY + ' .' + CLASS.axisYLabel),
-        axisY2Label = $$.main.select('.' + CLASS.axisY2 + ' .' + CLASS.axisY2Label);
-    (withTransition ? axisXLabel.transition() : axisXLabel)
-        .attr('x', this.xForXAxisLabel.bind(this))
-        .attr('dx', this.dxForXAxisLabel.bind(this))
-        .attr('dy', this.dyForXAxisLabel.bind(this))
-        .text(this.textForXAxisLabel.bind(this));
-    (withTransition ? axisYLabel.transition() : axisYLabel)
-        .attr('x', this.xForYAxisLabel.bind(this))
-        .attr('dx', this.dxForYAxisLabel.bind(this))
-        .attr('dy', this.dyForYAxisLabel.bind(this))
-        .text(this.textForYAxisLabel.bind(this));
-    (withTransition ? axisY2Label.transition() : axisY2Label)
-        .attr('x', this.xForY2AxisLabel.bind(this))
-        .attr('dx', this.dxForY2AxisLabel.bind(this))
-        .attr('dy', this.dyForY2AxisLabel.bind(this))
-        .text(this.textForY2AxisLabel.bind(this));
-};
-Axis.prototype.getPadding = function getPadding(padding, key, defaultValue, domainLength) {
-    const p = typeof padding === 'number' ? padding : padding[key];
-    if (!isValue(p)) {
-        return defaultValue;
-    }
-    if (padding.unit === 'ratio') {
-        return padding[key] * domainLength;
-    }
-    // assume padding is pixels if unit is not specified
-    return this.convertPixelsToAxisPadding(p, domainLength);
-};
-Axis.prototype.convertPixelsToAxisPadding = function convertPixelsToAxisPadding(pixels, domainLength) {
-    let $$ = this.owner,
-        length = $$.config.axis_rotated ? $$.width : $$.height;
-    return domainLength * (pixels / length);
-};
-Axis.prototype.generateTickValues = function generateTickValues(values, tickCount, forTimeSeries) {
-    let tickValues = values, targetCount, start, end, count, interval, i, tickValue;
-    if (tickCount) {
-        targetCount = isFunction(tickCount) ? tickCount() : tickCount;
-        // compute ticks according to tickCount
-        if (targetCount === 1) {
-            tickValues = [values[0]];
-        } else if (targetCount === 2) {
-            tickValues = [values[0], values[values.length - 1]];
-        } else if (targetCount > 2) {
-            count = targetCount - 2;
-            start = values[0];
-            end = values[values.length - 1];
-            interval = (end - start) / (count + 1);
-            // re-construct unique values
-            tickValues = [start];
-            for (i = 0; i < count; i++) {
-                tickValue = +start + interval * (i + 1);
-                tickValues.push(forTimeSeries ? new Date(tickValue) : tickValue);
-            }
-            tickValues.push(end);
-        }
-    }
-    if (!forTimeSeries) { tickValues = tickValues.sort((a, b) => { return a - b; }); }
-    return tickValues;
-};
-Axis.prototype.generateTransitions = function generateTransitions(duration) {
-    let $$ = this.owner, axes = $$.axes;
-    return {
-        axisX: duration ? axes.x.transition().duration(duration) : axes.x,
-        axisY: duration ? axes.y.transition().duration(duration) : axes.y,
-        axisY2: duration ? axes.y2.transition().duration(duration) : axes.y2,
-        axisSubX: duration ? axes.subx.transition().duration(duration) : axes.subx,
-    };
-};
-Axis.prototype.redraw = function redraw(transitions, isHidden) {
-    const $$ = this.owner;
-    $$.axes.x.style('opacity', isHidden ? 0 : 1);
-    $$.axes.y.style('opacity', isHidden ? 0 : 1);
-    $$.axes.y2.style('opacity', isHidden ? 0 : 1);
-    $$.axes.subx.style('opacity', isHidden ? 0 : 1);
-    transitions.axisX.call($$.xAxis);
-    transitions.axisY.call($$.yAxis);
-    transitions.axisY2.call($$.y2Axis);
-    transitions.axisSubX.call($$.subXAxis);
-};
-export {Axis};
-export default Axis;
\ No newline at end of file
diff --git a/es6_modules/axis/axis.js b/es6_modules/axis/axis.js
new file mode 100644
index 0000000..c8af33c
--- /dev/null
+++ b/es6_modules/axis/axis.js
@@ -0,0 +1,471 @@
+import {
+    CLASS,
+    isValue,
+    isFunction,
+    isString,
+    isEmpty,
+} from '../chartinternal';
+
+import { inherit, API } from './index';
+import c3_axis from './c3.axis';
+
+function Axis(owner) {
+    API.call(this, owner);
+}
+
+inherit(API, Axis);
+
+Axis.prototype.init = function init() {
+    const $$ = this.owner;
+    const config = $$.config;
+    const main = $$.main;
+    $$.axes.x = main.append('g')
+        .attr('class', CLASS.axis + ' ' + CLASS.axisX)
+        .attr('clip-path', $$.clipPathForXAxis)
+        .attr('transform', $$.getTranslate('x'))
+        .style('visibility', config.axis_x_show ? 'visible' : 'hidden');
+    $$.axes.x.append('text')
+        .attr('class', CLASS.axisXLabel)
+        .attr('transform', config.axis_rotated ? 'rotate(-90)' : '')
+        .style('text-anchor', this.textAnchorForXAxisLabel.bind(this));
+    $$.axes.y = main.append('g')
+        .attr('class', CLASS.axis + ' ' + CLASS.axisY)
+        .attr('clip-path', config.axis_y_inner ? '' : $$.clipPathForYAxis)
+        .attr('transform', $$.getTranslate('y'))
+        .style('visibility', config.axis_y_show ? 'visible' : 'hidden');
+    $$.axes.y.append('text')
+        .attr('class', CLASS.axisYLabel)
+        .attr('transform', config.axis_rotated ? '' : 'rotate(-90)')
+        .style('text-anchor', this.textAnchorForYAxisLabel.bind(this));
+
+    $$.axes.y2 = main.append('g')
+        .attr('class', CLASS.axis + ' ' + CLASS.axisY2)
+        // clip-path?
+        .attr('transform', $$.getTranslate('y2'))
+        .style('visibility', config.axis_y2_show ? 'visible' : 'hidden');
+    $$.axes.y2.append('text')
+        .attr('class', CLASS.axisY2Label)
+        .attr('transform', config.axis_rotated ? '' : 'rotate(-90)')
+        .style('text-anchor', this.textAnchorForY2AxisLabel.bind(this));
+};
+Axis.prototype.getXAxis = function getXAxis(
+    scale,
+    orient,
+    tickFormat,
+    tickValues,
+    withOuterTick,
+    withoutTransition,
+    withoutRotateTickText) {
+    const $$ = this.owner;
+    const config = $$.config;
+    const axisParams = {
+        isCategory: $$.isCategorized(),
+        withOuterTick,
+        tickMultiline: config.axis_x_tick_multiline,
+        tickWidth: config.axis_x_tick_width,
+        tickTextRotate: withoutRotateTickText ? 0 : config.axis_x_tick_rotate,
+        withoutTransition,
+    };
+    const axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient);
+
+    if ($$.isTimeSeries() && tickValues && typeof tickValues !== 'function') {
+        tickValues = tickValues.map(v => $$.parseDate(v));
+    }
+
+    // Set tick
+    axis.tickFormat(tickFormat).tickValues(tickValues);
+    if ($$.isCategorized()) {
+        axis.tickCentered(config.axis_x_tick_centered);
+        if (isEmpty(config.axis_x_tick_culling)) {
+            config.axis_x_tick_culling = false;
+        }
+    }
+
+    return axis;
+};
+Axis.prototype.updateXAxisTickValues = function updateXAxisTickValues(targets, axis) {
+    const $$ = this.owner;
+    const config = $$.config;
+    let tickValues;
+    if (config.axis_x_tick_fit || config.axis_x_tick_count) {
+        tickValues = this.generateTickValues(
+            $$.mapTargetsToUniqueXs(targets),
+            config.axis_x_tick_count,
+            $$.isTimeSeries()
+        );
+    }
+    if (axis) {
+        axis.tickValues(tickValues);
+    } else {
+        $$.xAxis.tickValues(tickValues);
+        $$.subXAxis.tickValues(tickValues);
+    }
+    return tickValues;
+};
+Axis.prototype.getYAxis = function getYAxis(scale,
+    orient,
+    tickFormat,
+    tickValues,
+    withOuterTick,
+    withoutTransition,
+    withoutRotateTickText) {
+    const $$ = this.owner;
+    const config = $$.config;
+    const axisParams = {
+        withOuterTick,
+        withoutTransition,
+        tickTextRotate: withoutRotateTickText ? 0 : config.axis_y_tick_rotate,
+    };
+    const axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient).tickFormat(tickFormat);
+    if ($$.isTimeSeriesY()) {
+        axis.ticks($$.d3.time[config.axis_y_tick_time_value], config.axis_y_tick_time_interval);
+    } else {
+        axis.tickValues(tickValues);
+    }
+    return axis;
+};
+Axis.prototype.getId = function getId(id) {
+    const config = this.owner.config;
+    return id in config.data_axes ? config.data_axes[id] : 'y';
+};
+Axis.prototype.getXAxisTickFormat = function getXAxisTickFormat() {
+    const $$ = this.owner;
+    const config = $$.config;
+    let format = $$.isTimeSeries() ? // eslint-disable-line no-nested-ternary
+        $$.defaultAxisTimeFormat :
+            $$.isCategorized() ?
+                $$.categoryName :
+                function (v) { return v < 0 ? v.toFixed(0) : v; };
+    if (config.axis_x_tick_format) {
+        if (isFunction(config.axis_x_tick_format)) {
+            format = config.axis_x_tick_format;
+        } else if ($$.isTimeSeries()) {
+            format = function (date) {
+                return date ? $$.axisTimeFormat(config.axis_x_tick_format)(date) : '';
+            };
+        }
+    }
+    return isFunction(format) ? function (v) { return format.call($$, v); } : format;
+};
+Axis.prototype.getTickValues = function getTickValues(tickValues, axis) {
+    return tickValues ? tickValues : // eslint-disable-line no-nested-ternary,no-unneeded-ternary
+        axis ? axis.tickValues() : undefined;
+};
+Axis.prototype.getXAxisTickValues = function getXAxisTickValues() {
+    return this.getTickValues(this.owner.config.axis_x_tick_values, this.owner.xAxis);
+};
+Axis.prototype.getYAxisTickValues = function getYAxisTickValues() {
+    return this.getTickValues(this.owner.config.axis_y_tick_values, this.owner.yAxis);
+};
+Axis.prototype.getY2AxisTickValues = function getY2AxisTickValues() {
+    return this.getTickValues(this.owner.config.axis_y2_tick_values, this.owner.y2Axis);
+};
+Axis.prototype.getLabelOptionByAxisId = function getLabelOptionByAxisId(axisId) {
+    const $$ = this.owner;
+    const config = $$.config;
+    let option;
+    if (axisId === 'y') {
+        option = config.axis_y_label;
+    } else if (axisId === 'y2') {
+        option = config.axis_y2_label;
+    } else if (axisId === 'x') {
+        option = config.axis_x_label;
+    }
+    return option;
+};
+Axis.prototype.getLabelText = function getLabelText(axisId) {
+    const option = this.getLabelOptionByAxisId(axisId);
+    return isString(option) ? option : option ? option.text : null; // eslint-disable-line no-nested-ternary,max-len
+};
+Axis.prototype.setLabelText = function setLabelText(axisId, text) {
+    const $$ = this.owner;
+    const config = $$.config;
+    const option = this.getLabelOptionByAxisId(axisId);
+    if (isString(option)) {
+        if (axisId === 'y') {
+            config.axis_y_label = text;
+        } else if (axisId === 'y2') {
+            config.axis_y2_label = text;
+        } else if (axisId === 'x') {
+            config.axis_x_label = text;
+        }
+    } else if (option) {
+        option.text = text;
+    }
+};
+Axis.prototype.getLabelPosition = function getLabelPosition(axisId, defaultPosition) {
+    const option = this.getLabelOptionByAxisId(axisId);
+    const position = (option && typeof option === 'object' && option.position) ? option.position : defaultPosition;
+    return {
+        isInner: position.indexOf('inner') >= 0,
+        isOuter: position.indexOf('outer') >= 0,
+        isLeft: position.indexOf('left') >= 0,
+        isCenter: position.indexOf('center') >= 0,
+        isRight: position.indexOf('right') >= 0,
+        isTop: position.indexOf('top') >= 0,
+        isMiddle: position.indexOf('middle') >= 0,
+        isBottom: position.indexOf('bottom') >= 0,
+    };
+};
+Axis.prototype.getXAxisLabelPosition = function getXAxisLabelPosition() {
+    return this.getLabelPosition('x', this.owner.config.axis_rotated ? 'inner-top' : 'inner-right');
+};
+Axis.prototype.getYAxisLabelPosition = function getYAxisLabelPosition() {
+    return this.getLabelPosition('y', this.owner.config.axis_rotated ? 'inner-right' : 'inner-top');
+};
+Axis.prototype.getY2AxisLabelPosition = function getY2AxisLabelPosition() {
+    return this.getLabelPosition('y2', this.owner.config.axis_rotated ? 'inner-right' : 'inner-top');
+};
+Axis.prototype.getLabelPositionById = function getLabelPositionById(id) {
+    return id === 'y2' ? this.getY2AxisLabelPosition() :
+        id === 'y' ? this.getYAxisLabelPosition() : this.getXAxisLabelPosition();
+};
+Axis.prototype.textForXAxisLabel = function textForXAxisLabel() {
+    return this.getLabelText('x');
+};
+Axis.prototype.textForYAxisLabel = function textForYAxisLabel() {
+    return this.getLabelText('y');
+};
+Axis.prototype.textForY2AxisLabel = function textForY2AxisLabel() {
+    return this.getLabelText('y2');
+};
+Axis.prototype.xForAxisLabel = function xForAxisLabel(forHorizontal, position) {
+    const $$ = this.owner;
+    if (forHorizontal) {
+        return position.isLeft ? 0 : position.isCenter ? $$.width / 2 : $$.width;
+    } else {
+        return position.isBottom ? -$$.height : position.isMiddle ? -$$.height / 2 : 0;
+    }
+};
+Axis.prototype.dxForAxisLabel = function dxForAxisLabel(forHorizontal, position) {
+    if (forHorizontal) {
+        return position.isLeft ? '0.5em' : position.isRight ? '-0.5em' : '0';
+    } else {
+        return position.isTop ? '-0.5em' : position.isBottom ? '0.5em' : '0';
+    }
+};
+Axis.prototype.textAnchorForAxisLabel = function textAnchorForAxisLabel(forHorizontal, position) {
+    if (forHorizontal) {
+        return position.isLeft ? 'start' : position.isCenter ? 'middle' : 'end';
+    } else {
+        return position.isBottom ? 'start' : position.isMiddle ? 'middle' : 'end';
+    }
+};
+Axis.prototype.xForXAxisLabel = function xForXAxisLabel() {
+    return this.xForAxisLabel(!this.owner.config.axis_rotated, this.getXAxisLabelPosition());
+};
+Axis.prototype.xForYAxisLabel = function xForYAxisLabel() {
+    return this.xForAxisLabel(this.owner.config.axis_rotated, this.getYAxisLabelPosition());
+};
+Axis.prototype.xForY2AxisLabel = function xForY2AxisLabel() {
+    return this.xForAxisLabel(this.owner.config.axis_rotated, this.getY2AxisLabelPosition());
+};
+Axis.prototype.dxForXAxisLabel = function dxForXAxisLabel() {
+    return this.dxForAxisLabel(!this.owner.config.axis_rotated, this.getXAxisLabelPosition());
+};
+Axis.prototype.dxForYAxisLabel = function dxForYAxisLabel() {
+    return this.dxForAxisLabel(this.owner.config.axis_rotated, this.getYAxisLabelPosition());
+};
+Axis.prototype.dxForY2AxisLabel = function dxForY2AxisLabel() {
+    return this.dxForAxisLabel(this.owner.config.axis_rotated, this.getY2AxisLabelPosition());
+};
+Axis.prototype.dyForXAxisLabel = function dyForXAxisLabel() {
+    const $$ = this.owner;
+    const config = $$.config;
+    const position = this.getXAxisLabelPosition();
+    if (config.axis_rotated) {
+        return position.isInner ? '1.2em' : -25 - this.getMaxTickWidth('x');
+    } else {
+        return position.isInner ? '-0.5em' : config.axis_x_height ? config.axis_x_height - 10 : '3em';
+    }
+};
+Axis.prototype.dyForYAxisLabel = function dyForYAxisLabel() {
+    const $$ = this.owner;
+    const position = this.getYAxisLabelPosition();
+    if ($$.config.axis_rotated) {
+        return position.isInner ? '-0.5em' : '3em';
+    } else {
+        return position.isInner ? '1.2em' : -10 - ($$.config.axis_y_inner ? 0 : (this.getMaxTickWidth('y') + 10));
+    }
+};
+Axis.prototype.dyForY2AxisLabel = function dyForY2AxisLabel() {
+    const $$ = this.owner;
+    const position = this.getY2AxisLabelPosition();
+    if ($$.config.axis_rotated) {
+        return position.isInner ? '1.2em' : '-2.2em';
+    } else {
+        return position.isInner ? '-0.5em' : 15 + ($$.config.axis_y2_inner ? 0 : (this.getMaxTickWidth('y2') + 15));
+    }
+};
+Axis.prototype.textAnchorForXAxisLabel = function textAnchorForXAxisLabel() {
+    const $$ = this.owner;
+    return this.textAnchorForAxisLabel(!$$.config.axis_rotated, this.getXAxisLabelPosition());
+};
+Axis.prototype.textAnchorForYAxisLabel = function textAnchorForYAxisLabel() {
+    const $$ = this.owner;
+    return this.textAnchorForAxisLabel($$.config.axis_rotated, this.getYAxisLabelPosition());
+};
+Axis.prototype.textAnchorForY2AxisLabel = function textAnchorForY2AxisLabel() {
+    const $$ = this.owner;
+    return this.textAnchorForAxisLabel($$.config.axis_rotated, this.getY2AxisLabelPosition());
+};
+Axis.prototype.getMaxTickWidth = function getMaxTickWidth(id, withoutRecompute) {
+    const $$ = this.owner;
+    const config = $$.config;
+    let maxWidth = 0;
+    let targetsToShow;
+    let scale;
+    let axis;
+    let dummy;
+    let svg;
+    if (withoutRecompute && $$.currentMaxTickWidths[id]) {
+        return $$.currentMaxTickWidths[id];
+    }
+    if ($$.svg) {
+        targetsToShow = $$.filterTargetsToShow($$.data.targets);
+        if (id === 'y') {
+            scale = $$.y.copy().domain($$.getYDomain(targetsToShow, 'y'));
+            axis = this.getYAxis(
+                scale,
+                $$.yOrient,
+                config.axis_y_tick_format,
+                $$.yAxisTickValues,
+                false,
+                true,
+                true
+            );
+        } else if (id === 'y2') {
+            scale = $$.y2.copy().domain($$.getYDomain(targetsToShow, 'y2'));
+            axis = this.getYAxis(
+                scale,
+                $$.y2Orient,
+                config.axis_y2_tick_format,
+                $$.y2AxisTickValues,
+                false,
+                true,
+                true
+            );
+        } else {
+            scale = $$.x.copy().domain($$.getXDomain(targetsToShow));
+            axis = this.getXAxis(
+                scale,
+                $$.xOrient,
+                $$.xAxisTickFormat,
+                $$.xAxisTickValues,
+                false,
+                true,
+                true
+            );
+            this.updateXAxisTickValues(targetsToShow, axis);
+        }
+        dummy = $$.d3.select('body').append('div').classed('c3', true);
+        svg = dummy.append('svg')
+            .style('visibility', 'hidden')
+            .style('position', 'fixed')
+            .style('top', 0)
+            .style('left', 0);
+        svg.append('g').call(axis).each(function () {
+            $$.d3.select(this).selectAll('text').each(function () {
+                const box = this.getBoundingClientRect();
+                if (maxWidth < box.width) { maxWidth = box.width; }
+            });
+            dummy.remove();
+        });
+    }
+    $$.currentMaxTickWidths[id] = maxWidth <= 0 ? $$.currentMaxTickWidths[id] : maxWidth;
+    return $$.currentMaxTickWidths[id];
+};
+
+Axis.prototype.updateLabels = function updateLabels(withTransition) {
+    const $$ = this.owner;
+    const axisXLabel = $$.main.select('.' + CLASS.axisX + ' .' + CLASS.axisXLabel);
+    const axisYLabel = $$.main.select('.' + CLASS.axisY + ' .' + CLASS.axisYLabel);
+    const axisY2Label = $$.main.select('.' + CLASS.axisY2 + ' .' + CLASS.axisY2Label);
+    (withTransition ? axisXLabel.transition() : axisXLabel)
+        .attr('x', this.xForXAxisLabel.bind(this))
+        .attr('dx', this.dxForXAxisLabel.bind(this))
+        .attr('dy', this.dyForXAxisLabel.bind(this))
+        .text(this.textForXAxisLabel.bind(this));
+    (withTransition ? axisYLabel.transition() : axisYLabel)
+        .attr('x', this.xForYAxisLabel.bind(this))
+        .attr('dx', this.dxForYAxisLabel.bind(this))
+        .attr('dy', this.dyForYAxisLabel.bind(this))
+        .text(this.textForYAxisLabel.bind(this));
+    (withTransition ? axisY2Label.transition() : axisY2Label)
+        .attr('x', this.xForY2AxisLabel.bind(this))
+        .attr('dx', this.dxForY2AxisLabel.bind(this))
+        .attr('dy', this.dyForY2AxisLabel.bind(this))
+        .text(this.textForY2AxisLabel.bind(this));
+};
+Axis.prototype.getPadding = function getPadding(padding, key, defaultValue, domainLength) {
+    const p = typeof padding === 'number' ? padding : padding[key];
+    if (!isValue(p)) {
+        return defaultValue;
+    }
+    if (padding.unit === 'ratio') {
+        return padding[key] * domainLength;
+    }
+    // assume padding is pixels if unit is not specified
+    return this.convertPixelsToAxisPadding(p, domainLength);
+};
+Axis.prototype.convertPixelsToAxisPadding = function convertPixelsToAxisPadding(pixels, domainLength) { // eslint-disable-line max-len
+    const $$ = this.owner;
+    const length = $$.config.axis_rotated ? $$.width : $$.height;
+    return domainLength * (pixels / length);
+};
+Axis.prototype.generateTickValues = function generateTickValues(values, tickCount, forTimeSeries) {
+    let tickValues = values;
+    let targetCount;
+    let start;
+    let end;
+    let count;
+    let interval;
+    let i;
+    let tickValue;
+    if (tickCount) {
+        targetCount = isFunction(tickCount) ? tickCount() : tickCount;
+        // compute ticks according to tickCount
+        if (targetCount === 1) {
+            tickValues = [values[0]];
+        } else if (targetCount === 2) {
+            tickValues = [values[0], values[values.length - 1]];
+        } else if (targetCount > 2) {
+            count = targetCount - 2;
+            start = values[0];
+            end = values[values.length - 1];
+            interval = (end - start) / (count + 1);
+            // re-construct unique values
+            tickValues = [start];
+            for (i = 0; i < count; i++) {
+                tickValue = +start + interval * (i + 1);
+                tickValues.push(forTimeSeries ? new Date(tickValue) : tickValue);
+            }
+            tickValues.push(end);
+        }
+    }
+    if (!forTimeSeries) { tickValues = tickValues.sort((a, b) => a - b); }
+    return tickValues;
+};
+Axis.prototype.generateTransitions = function generateTransitions(duration) {
+    let $$ = this.owner;
+    let axes = $$.axes;
+    return {
+        axisX: duration ? axes.x.transition().duration(duration) : axes.x,
+        axisY: duration ? axes.y.transition().duration(duration) : axes.y,
+        axisY2: duration ? axes.y2.transition().duration(duration) : axes.y2,
+        axisSubX: duration ? axes.subx.transition().duration(duration) : axes.subx,
+    };
+};
+Axis.prototype.redraw = function redraw(transitions, isHidden) {
+    const $$ = this.owner;
+    $$.axes.x.style('opacity', isHidden ? 0 : 1);
+    $$.axes.y.style('opacity', isHidden ? 0 : 1);
+    $$.axes.y2.style('opacity', isHidden ? 0 : 1);
+    $$.axes.subx.style('opacity', isHidden ? 0 : 1);
+    transitions.axisX.call($$.xAxis);
+    transitions.axisY.call($$.yAxis);
+    transitions.axisY2.call($$.y2Axis);
+    transitions.axisSubX.call($$.subXAxis);
+};
+
+export default Axis;
diff --git a/es6_modules/axis/c3.axis.js b/es6_modules/axis/c3.axis.js
new file mode 100644
index 0000000..2622f72
--- /dev/null
+++ b/es6_modules/axis/c3.axis.js
@@ -0,0 +1,351 @@
+let tickTextCharSize;
+function c3_axis(d3, params) {
+    let scale = d3.scale.linear();
+    let orient = 'bottom';
+    const innerTickSize = 6;
+    const tickPadding = 3;
+    let tickValues = null;
+    let tickFormat;
+    let tickArguments;
+
+    let tickOffset = 0;
+    let tickCulling = true;
+    let tickCentered;
+
+    params = params || {};
+
+    const outerTickSize = params.withOuterTick ? 6 : 0;
+
+    function axisX(selection, x) {
+        selection.attr('transform', d => 'translate(' + Math.ceil(x(d) + tickOffset) + ', 0)');
+    }
+    function axisY(selection, y) {
+        selection.attr('transform', d => 'translate(0,' + Math.ceil(y(d)) + ')');
+    }
+    function scaleExtent(domain) {
+        const start = domain[0];
+        const stop = domain[domain.length - 1];
+        return start < stop ? [start, stop] : [stop, start];
+    }
+    function generateTicks(scale) { // eslint-disable-line no-shadow
+        let i;
+        const ticks = [];
+        if (scale.ticks) {
+            return scale.ticks.apply(scale, tickArguments);
+        }
+        const domain = scale.domain();
+        for (i = Math.ceil(domain[0]); i < domain[1]; i++) {
+            ticks.push(i);
+        }
+        if (ticks.length > 0 && ticks[0] > 0) {
+            ticks.unshift(ticks[0] - (ticks[1] - ticks[0]));
+        }
+        return ticks;
+    }
+    function copyScale() {
+        const newScale = scale.copy();
+        let domain;
+        if (params.isCategory) {
+            domain = scale.domain();
+            newScale.domain([domain[0], domain[1] - 1]);
+        }
+        return newScale;
+    }
+    function textFormatted(v) {
+        const formatted = tickFormat ? tickFormat(v) : v;
+        return typeof formatted !== 'undefined' ? formatted : '';
+    }
+    function getSizeFor1Char(tick) {
+        if (tickTextCharSize) {
+            return tickTextCharSize;
+        }
+        const size = {
+            h: 11.5,
+            w: 5.5,
+        };
+        tick.select('text').text(textFormatted).each(function (d) {
+            let box = this.getBoundingClientRect(),
+                text = textFormatted(d),
+                h = box.height,
+                w = text ? (box.width / text.length) : undefined;
+            if (h && w) {
+                size.h = h;
+                size.w = w;
+            }
+        }).text('');
+        tickTextCharSize = size;
+        return size;
+    }
+    function transitionise(selection) {
+        return params.withoutTransition ? selection : d3.transition(selection);
+    }
+    function axis(g) {
+        g.each(function () {
+            const g = axis.g = d3.select(this);
+
+            let scale0 = this.__chart__ || scale,
+                scale1 = this.__chart__ = copyScale();
+
+            let ticks = tickValues || generateTicks(scale1),
+                tick = g.selectAll('.tick').data(ticks, scale1),
+                tickEnter = tick.enter().insert('g', '.domain').attr('class', 'tick').style('opacity', 1e-6),
+                // MEMO: No exit transition. The reason is this transition affects max tick width
+                // calculation because old tick will be included in the ticks.
+                tickExit = tick.exit().remove(),
+                tickUpdate = transitionise(tick).style('opacity', 1),
+                tickTransform,
+                tickX,
+                tickY;
+
+            let range = scale.rangeExtent ? scale.rangeExtent() : scaleExtent(scale.range()),
+                path = g.selectAll('.domain').data([0]),
+                pathUpdate = (path.enter().append('path').attr('class', 'domain'), transitionise(path));
+            tickEnter.append('line');
+            tickEnter.append('text');
+
+            let lineEnter = tickEnter.select('line'),
+                lineUpdate = tickUpdate.select('line'),
+                textEnter = tickEnter.select('text'),
+                textUpdate = tickUpdate.select('text');
+
+            if (params.isCategory) {
+                tickOffset = Math.ceil((scale1(1) - scale1(0)) / 2);
+                tickX = tickCentered ? 0 : tickOffset;
+                tickY = tickCentered ? tickOffset : 0;
+            } else {
+                tickOffset = tickX = 0;
+            }
+
+            let text,
+                tspan,
+                sizeFor1Char = getSizeFor1Char(g.select('.tick')),
+                counts = [];
+
+            let tickLength = Math.max(innerTickSize, 0) + tickPadding,
+                isVertical = orient === 'left' || orient === 'right';
+
+            // this should be called only when category axis
+            function splitTickText(d, maxWidth) {
+                let tickText = textFormatted(d),
+                    subtext,
+                    spaceIndex,
+                    textWidth,
+                    splitted = [];
+
+                if (Object.prototype.toString.call(tickText) === '[object Array]') {
+                    return tickText;
+                }
+
+                if (!maxWidth || maxWidth <= 0) {
+                    maxWidth = isVertical ? 95 :
+                    params.isCategory ?
+                        (Math.ceil(scale1(ticks[1]) - scale1(ticks[0])) - 12) : 110;
+                }
+
+                function split(splitted, text) {
+                    spaceIndex = undefined;
+                    for (let i = 1; i < text.length; i++) {
+                        if (text.charAt(i) === ' ') {
+                            spaceIndex = i;
+                        }
+                        subtext = text.substr(0, i + 1);
+                        textWidth = sizeFor1Char.w * subtext.length;
+                        // if text width gets over tick width, split by space index or crrent index
+                        if (maxWidth < textWidth) {
+                            return split(
+                                splitted.concat(text.substr(0, spaceIndex || i)),
+                                text.slice(spaceIndex ? spaceIndex + 1 : i)
+                            );
+                        }
+                    }
+                    return splitted.concat(text);
+                }
+
+                return split(splitted, tickText + '');
+            }
+
+            function tspanDy(d, i) {
+                let dy = sizeFor1Char.h;
+                if (i === 0) {
+                    if (orient === 'left' || orient === 'right') {
+                        dy = -((counts[d.index] - 1) * (sizeFor1Char.h / 2) - 3);
+                    } else {
+                        dy = '.71em';
+                    }
+                }
+                return dy;
+            }
+
+            function tickSize(d) {
+                const tickPosition = scale(d) + (tickCentered ? 0 : tickOffset);
+                return range[0] < tickPosition && tickPosition < range[1] ? innerTickSize : 0;
+            }
+
+            text = tick.select('text');
+            tspan = text.selectAll('tspan')
+                .data((d, i) => {
+                    const splitted = params.tickMultiline ?
+                        splitTickText(d, params.tickWidth) :
+                        [].concat(textFormatted(d));
+                    counts[i] = splitted.length;
+                    return splitted.map(s => ({ index: i, splitted: s }));
+                });
+            tspan.enter().append('tspan');
+            tspan.exit().remove();
+            tspan.text(d => d.splitted);
+
+            const rotate = params.tickTextRotate;
+
+            function textAnchorForText(rotate) {
+                if (!rotate) {
+                    return 'middle';
+                }
+                return rotate > 0 ? 'start' : 'end';
+            }
+            function textTransform(rotate) {
+                if (!rotate) {
+                    return '';
+                }
+                return 'rotate(' + rotate + ')';
+            }
+            function dxForText(rotate) {
+                if (!rotate) {
+                    return 0;
+                }
+                return 8 * Math.sin(Math.PI * (rotate / 180));
+            }
+            function yForText(rotate) {
+                if (!rotate) {
+                    return tickLength;
+                }
+                return 11.5 - 2.5 * (rotate / 15) * (rotate > 0 ? 1 : -1);
+            }
+
+            switch (orient) {
+            case 'bottom':
+                {
+                    tickTransform = axisX;
+                    lineEnter.attr('y2', innerTickSize);
+                    textEnter.attr('y', tickLength);
+                    lineUpdate.attr('x1', tickX).attr('x2', tickX).attr('y2', tickSize);
+                    textUpdate.attr('x', 0).attr('y', yForText(rotate))
+                        .style('text-anchor', textAnchorForText(rotate))
+                        .attr('transform', textTransform(rotate));
+                    tspan.attr('x', 0).attr('dy', tspanDy).attr('dx', dxForText(rotate));
+                    pathUpdate.attr('d', 'M' + range[0] + ',' + outerTickSize + 'V0H' + range[1] + 'V' + outerTickSize);
+                    break;
+                }
+            case 'top':
+                {
+                    // TODO: rotated tick text
+                    tickTransform = axisX;
+                    lineEnter.attr('y2', -innerTickSize);
+                    textEnter.attr('y', -tickLength);
+                    lineUpdate.attr('x2', 0).attr('y2', -innerTickSize);
+                    textUpdate.attr('x', 0).attr('y', -tickLength);
+                    text.style('text-anchor', 'middle');
+                    tspan.attr('x', 0).attr('dy', '0em');
+                    pathUpdate.attr('d', 'M' + range[0] + ',' + -outerTickSize + 'V0H' + range[1] + 'V' + -outerTickSize);
+                    break;
+                }
+            case 'left':
+                {
+                    tickTransform = axisY;
+                    lineEnter.attr('x2', -innerTickSize);
+                    textEnter.attr('x', -tickLength);
+                    lineUpdate.attr('x2', -innerTickSize).attr('y1', tickY).attr('y2', tickY);
+                    textUpdate.attr('x', -tickLength).attr('y', tickOffset);
+                    text.style('text-anchor', 'end');
+                    tspan.attr('x', -tickLength).attr('dy', tspanDy);
+                    pathUpdate.attr('d', 'M' + -outerTickSize + ',' + range[0] + 'H0V' + range[1] + 'H' + -outerTickSize);
+                    break;
+                }
+            case 'right':
+                {
+                    tickTransform = axisY;
+                    lineEnter.attr('x2', innerTickSize);
+                    textEnter.attr('x', tickLength);
+                    lineUpdate.attr('x2', innerTickSize).attr('y2', 0);
+                    textUpdate.attr('x', tickLength).attr('y', 0);
+                    text.style('text-anchor', 'start');
+                    tspan.attr('x', tickLength).attr('dy', tspanDy);
+                    pathUpdate.attr('d', 'M' + outerTickSize + ',' + range[0] + 'H0V' + range[1] + 'H' + outerTickSize);
+                    break;
+                }
+            default:
+                break;
+            }
+            if (scale1.rangeBand) {
+                let x = scale1,
+                    dx = x.rangeBand() / 2;
+                scale0 = scale1 = function (d) {
+                    return x(d) + dx;
+                };
+            } else if (scale0.rangeBand) {
+                scale0 = scale1;
+            } else {
+                tickExit.call(tickTransform, scale1);
+            }
+            tickEnter.call(tickTransform, scale0);
+            tickUpdate.call(tickTransform, scale1);
+        });
+    }
+    axis.scale = function (x) {
+        if (!arguments.length) { return scale; }
+        scale = x;
+        return axis;
+    };
+    axis.orient = function (x) {
+        if (!arguments.length) { return orient; }
+        orient = x in { top: 1, right: 1, bottom: 1, left: 1 } ? x + '' : 'bottom';
+        return axis;
+    };
+    axis.tickFormat = function (format) {
+        if (!arguments.length) { return tickFormat; }
+        tickFormat = format;
+        return axis;
+    };
+    axis.tickCentered = function (isCentered) {
+        if (!arguments.length) { return tickCentered; }
+        tickCentered = isCentered;
+        return axis;
+    };
+    axis.tickOffset = function () {
+        return tickOffset;
+    };
+    axis.tickInterval = function () {
+        let interval,
+            length;
+        if (params.isCategory) {
+            interval = tickOffset * 2;
+        } else {
+            length = axis.g.select('path.domain').node().getTotalLength() - outerTickSize * 2;
+            interval = length / axis.g.selectAll('line').size();
+        }
+        return interval === Infinity ? 0 : interval;
+    };
+    axis.ticks = function (...args) {
+        if (!arguments.length) { return tickArguments; }
+        tickArguments = args;
+        return axis;
+    };
+    axis.tickCulling = function (culling) {
+        if (!arguments.length) { return tickCulling; }
+        tickCulling = culling;
+        return axis;
+    };
+    axis.tickValues = function (x) {
+        if (typeof x === 'function') {
+            tickValues = function () {
+                return x(scale.domain());
+            };
+        } else {
+            if (!arguments.length) { return tickValues; }
+            tickValues = x;
+        }
+        return axis;
+    };
+    return axis;
+}
+
+export default c3_axis;
diff --git a/es6_modules/axis/index.js b/es6_modules/axis/index.js
new file mode 100644
index 0000000..5704553
--- /dev/null
+++ b/es6_modules/axis/index.js
@@ -0,0 +1,41 @@
+// import {
+//     CLASS,
+//     isValue,
+//     isFunction,
+//     isString,
+//     isUndefined,
+//     isDefined,
+//     ceil10,
+//     asHalfPixel,
+//     diffDomain,
+//     isEmpty,
+//     notEmpty,
+//     getOption,
+//     hasValue,
+//     sanitise,
+//     getPathBox,
+//     ChartInternal } from '../chartinternal';
+
+import Axis from './axis';
+
+function API(owner) {
+    this.owner = owner;
+}
+
+/* eslint-disable */
+function inherit(base, derived) {
+    if (Object.create) {
+        derived.prototype = Object.create(base.prototype);
+    } else {
+        const f = function f() {};
+        f.prototype = base.prototype;
+        derived.prototype = new f();
+    }
+
+    derived.prototype.constructor = derived;
+
+    return derived;
+}
+/* eslint-enable */
+
+export { API, inherit, Axis };
diff --git a/es6_modules/chart.js b/es6_modules/chart.js
index bc0edf2..f29f280 100644
--- a/es6_modules/chart.js
+++ b/es6_modules/chart.js
@@ -1,4 +1,10 @@
-import {CLASS,isValue,isFunction,isString,isUndefined,isDefined,ceil10,asHalfPixel,diffDomain,isEmpty,notEmpty,getOption,hasValue,sanitise,getPathBox, ChartInternal} from './chartinternal.js';
+import { CLASS,
+    isValue,
+    isUndefined,
+    isDefined,
+    ChartInternal,
+} from './chartinternal.js';
+
 let c3_chart_fn;
 
 
@@ -760,5 +766,5 @@ c3_chart_fn.tooltip.hide = function () {
 
     this.internal.config.tooltip_onhide.call(this);
 };
-export {Chart};
-export default Chart;
\ No newline at end of file
+export { Chart };
+export default Chart;
diff --git a/es6_modules/chartinternal.js b/es6_modules/chartinternal.js
index 4dbcf69..b9023f8 100644
--- a/es6_modules/chartinternal.js
+++ b/es6_modules/chartinternal.js
@@ -1,5 +1,7 @@
-import {Axis} from './axis.js';
+import { Axis } from './axis/index';
+
 import d3 from 'd3';
+
 function ChartInternal(api) {
     const $$ = this;
     $$.d3 = window.d3 ? window.d3 : typeof require !== 'undefined' ? require('d3') : undefined;
@@ -5938,4 +5940,4 @@ c3_chart_internal_fn.isChrome = function () {
     return ua.indexOf('Chrome') >= 0;
 };
 export {CLASS,isValue,isFunction,isString,isUndefined,isDefined,ceil10,asHalfPixel,diffDomain,isEmpty,notEmpty,getOption,hasValue,sanitise,getPathBox, ChartInternal};
-export default ChartIntenal;
\ No newline at end of file
+export default ChartIntenal;
diff --git a/es6_modules/rollup.entry.js b/es6_modules/rollup.entry.js
index 1c47d13..a19db85 100644
--- a/es6_modules/rollup.entry.js
+++ b/es6_modules/rollup.entry.js
@@ -1,31 +1,32 @@
-// This file is only the entry point for rollup
-import {
-    ChartInternal
-} from './chartinternal.js';
-import {
-    Chart
-} from './chart.js';
-import {
-    Axis
-} from './axis.js';
+/**
+ * C3.js
+ * (c) 2016 Masayuki Tanaka and the C3.js contributors (See package.json)
+ * License: MIT
+ */
 
+import { ChartInternal } from './chartinternal.js';
+import { Chart } from './chart.js';
+import { Axis } from './axis/index';
 
-var version = "0.4.11",
-    generate = function(config) {
-        return new Chart(config);
+
+const version = '0.4.11';
+
+const generate = function generate(config) {
+    return new Chart(config);
+};
+
+const chart = {
+    fn: Chart.prototype,
+    internal: {
+        fn: ChartInternal.prototype,
+        axis: {
+            fn: Axis.prototype,
+        },
     },
-    chart = {
-        fn: Chart.prototype,
-        internal: {
-            fn: ChartInternal.prototype,
-            axis: {
-                fn: Axis.prototype
-            }
-        }
-    };
+};
 
 export {
     version,
     generate,
-    chart
-}
+    chart,
+};