diff --git a/.jshintrc b/.jshintrc
index b0fcc7c..4b465d4 100644
--- a/.jshintrc
+++ b/.jshintrc
@@ -8,7 +8,7 @@
     "undef": true,
     "unused": true,
     "indent": 4,
-
+    "esversion": 6,
     "eqnull": true,
     "expr": true,
     "newcap": false,
diff --git a/Gruntfile.coffee b/Gruntfile.coffee
index 745bf2a..67317e5 100644
--- a/Gruntfile.coffee
+++ b/Gruntfile.coffee
@@ -8,7 +8,7 @@ module.exports = (grunt) ->
             files: ['src/scss/*.scss']
 
         jshint:
-          c3: 'c3.js'
+          c3: 'src/**/*.js'
           spec: 'spec/*.js'
           options:
             reporter: require('jshint-stylish')
diff --git a/package.json b/package.json
index 4fe368e..5f7fba8 100644
--- a/package.json
+++ b/package.json
@@ -37,7 +37,7 @@
     "grunt-contrib-uglify": "~0.4.0",
     "grunt-contrib-watch": "^0.6.1",
     "grunt-karma": "^0.12.1",
-    "grunt-sass": "^1.0.0",
+    "grunt-sass": "^2.0.0",
     "jasmine-core": "^2.3.4",
     "jshint-stylish": "^2.1.0",
     "karma": "^0.13.10",
diff --git a/src/api.region.js b/src/api.region.js
index 14d5bce..73d6a03 100644
--- a/src/api.region.js
+++ b/src/api.region.js
@@ -1,6 +1,5 @@
 import CLASS from './class';
 import { c3_chart_fn } from './core';
-import { getOption } from './util';
 
 c3_chart_fn.regions = function (regions) {
     var $$ = this.internal, config = $$.config;
diff --git a/src/axis.js b/src/axis.js
index 982af2d..dbf784c 100644
--- a/src/axis.js
+++ b/src/axis.js
@@ -1,7 +1,7 @@
 import CLASS from './class';
-import { inherit, API } from './core'
+import { inherit, API } from './core';
 import { isValue, isFunction, isString, isEmpty } from './util';
-import c3_axis from './c3.axis'
+import c3_axis from './c3.axis';
 
 export default function Axis(owner) {
     API.call(this, owner);
diff --git a/src/class-utils.js b/src/class-utils.js
index 63d54e9..741cd01 100644
--- a/src/class-utils.js
+++ b/src/class-utils.js
@@ -1,4 +1,4 @@
-import CLASS from './class'
+import CLASS from './class';
 import { c3_chart_internal_fn } from './core';
 
 c3_chart_internal_fn.generateClass = function (prefix, targetId) {
diff --git a/src/core.js b/src/core.js
index 415aa9e..909aa5f 100644
--- a/src/core.js
+++ b/src/core.js
@@ -1,3 +1,4 @@
+import * as d3 from 'd3';
 import Axis from './axis';
 import CLASS from './class';
 import { isValue, isFunction, isString, isUndefined, isDefined, ceil10, asHalfPixel, diffDomain, isEmpty, notEmpty, getOption, hasValue, sanitise, getPathBox } from './util';
@@ -8,8 +9,6 @@ export var c3_chart_fn;
 export var c3_chart_internal_fn;
 export var c3_chart_internal_axis_fn;
 
-var d3 = window.d3 ? window.d3 : typeof require !== 'undefined' ? require("d3") : undefined;
-
 export function API(owner) {
     this.owner = owner;
 }
@@ -50,7 +49,7 @@ function Chart(config) {
 
 function ChartInternal(api) {
     var $$ = this;
-    $$.d3 = d3
+    $$.d3 = d3;
     $$.api = api;
     $$.config = $$.getDefaultConfig();
     $$.data = {};
@@ -1084,4 +1083,3 @@ c3_chart_internal_fn.hasValue = hasValue;
 c3_chart_internal_fn.sanitise = sanitise;
 c3_chart_internal_fn.getPathBox = getPathBox;
 c3_chart_internal_fn.CLASS = CLASS;
-
diff --git a/src/index.js b/src/index.js
index dd9cbeb..c09cd6f 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,4 +1,4 @@
-import { c3 } from './core'
+import { c3 } from './core';
 
 import './polyfill';
 
@@ -55,4 +55,4 @@ import './ua';
 import './util';
 import './zoom';
 
-export default c3
+export default c3;
diff --git a/src/title.js b/src/title.js
index 6c198c5..863f6ca 100644
--- a/src/title.js
+++ b/src/title.js
@@ -1,4 +1,3 @@
-import CLASS from './class';
 import { c3_chart_internal_fn } from './core';
 
 c3_chart_internal_fn.initTitle = function () {