diff --git a/src/api.tooltip.js b/src/api.tooltip.js
index 5ade853..244ede3 100644
--- a/src/api.tooltip.js
+++ b/src/api.tooltip.js
@@ -1,5 +1,4 @@
 import { c3_chart_fn } from './core';
-import { isValue } from './util';
 
 c3_chart_fn.tooltip = function () {};
 c3_chart_fn.tooltip.show = function (args) {
diff --git a/src/axis.js b/src/axis.js
index 64f6096..3593635 100644
--- a/src/axis.js
+++ b/src/axis.js
@@ -223,8 +223,8 @@ c3_axis_internal_fn.generateAxis = function () {
                     return internal.tspanData(d, i, scale1);
                 }),
                 tspanEnter = tspans.enter().append('tspan'),
-                tspanExit = tspans.exit().remove(),
                 tspanUpdate = tspanEnter.merge(tspans).text(function (d) { return d.splitted; });
+            tspans.exit().remove();
 
             var path = g.selectAll(".domain").data([ 0 ]),
                 pathUpdate = path.enter().append("path").merge(path).attr("class", "domain");
diff --git a/src/shape.js b/src/shape.js
index 8afe738..b0f403f 100644
--- a/src/shape.js
+++ b/src/shape.js
@@ -98,13 +98,13 @@ c3_chart_internal_fn.getInterpolate = function (d) {
         type;
 
     if ($$.isSplineType(d)) {
-        type = types[$$.config.spline_interpolation_type] || types['cardinal'];
+        type = types[$$.config.spline_interpolation_type] || types.cardinal;
     }
     else if ($$.isStepType(d)) {
         type = types[$$.config.line_step_type];
     }
     else {
-        type = types["linear"];
+        type = types.linear;
     }
     return type;
 };
diff --git a/src/subchart.js b/src/subchart.js
index e76f17e..ee6f956 100644
--- a/src/subchart.js
+++ b/src/subchart.js
@@ -143,7 +143,7 @@ c3_chart_internal_fn.updateBarForSubchart = function (durationForExit) {
         .attr("class", $$.classBar.bind($$))
         .style("stroke", 'none')
         .style("fill", $$.color);
-    var contextBarExit = contextBar.exit().transition().duration(durationForExit)
+    contextBar.exit().transition().duration(durationForExit)
         .style('opacity', 0)
         .remove();
     $$.contextBar = contextBarEnter.merge(contextBar)
@@ -161,7 +161,7 @@ c3_chart_internal_fn.updateLineForSubchart = function (durationForExit) {
     var contextLineEnter = contextLine.enter().append('path')
         .attr('class', $$.classLine.bind($$))
         .style('stroke', $$.color);
-    var contextLineExit = contextLine.exit().transition().duration(durationForExit)
+    contextLine.exit().transition().duration(durationForExit)
         .style('opacity', 0)
         .remove();
     $$.contextLine = contextLineEnter.merge(contextLine)
@@ -180,7 +180,7 @@ c3_chart_internal_fn.updateAreaForSubchart = function (durationForExit) {
         .attr("class", $$.classArea.bind($$))
         .style("fill", $$.color)
         .style("opacity", function () { $$.orgAreaOpacity = +d3.select(this).style('opacity'); return 0; });
-    var contextAreaExit = contextArea.exit().transition().duration(durationForExit)
+    contextArea.exit().transition().duration(durationForExit)
         .style('opacity', 0)
         .remove();
     $$.contextArea = contextAreaEnter.merge(contextArea)
diff --git a/src/text.js b/src/text.js
index d0dcf67..38f0d74 100644
--- a/src/text.js
+++ b/src/text.js
@@ -20,7 +20,7 @@ c3_chart_internal_fn.updateTargetsForText = function (targets) {
         .style("pointer-events", "none");
     mainTextEnter.append('g')
         .attr('class', classTexts);
-    var mainTextUpdate = mainTextEnter.merge(mainText)
+    mainTextEnter.merge(mainText)
         .attr('class', function (d) { return classChartText(d) + classFocus(d); });
 };
 c3_chart_internal_fn.updateText = function (xForText, yForText, durationForExit) {
diff --git a/src/zoom.js b/src/zoom.js
index 2dcab41..446347c 100644
--- a/src/zoom.js
+++ b/src/zoom.js
@@ -1,6 +1,4 @@
-import CLASS from './class';
 import { c3_chart_internal_fn } from './core';
-import { diffDomain } from './util';
 
 c3_chart_internal_fn.initZoom = function () {
     var $$ = this, d3 = $$.d3, config = $$.config, startEvent;