diff --git a/README.md b/README.md
index d9cf112..cff694b 100644
--- a/README.md
+++ b/README.md
@@ -96,7 +96,7 @@ under html root element.
 For more information, please check the [documentation](doc/API.md).
 
 ```javascript
-var el = document.createElement('div');
+let el = document.createElement('div');
 document.body.appendChild(el);
 
 eruda.init({
diff --git a/doc/API.md b/doc/API.md
index dd064e6..de904ee 100644
--- a/doc/API.md
+++ b/doc/API.md
@@ -14,7 +14,7 @@ Initialize eruda.
 |useShadowDom=true|boolean     |Use shadow dom for css encapsulation                                                     |
 
 ```javascript
-var el = document.createElement('div');
+let el = document.createElement('div');
 document.body.appendChild(el);
 
 eruda.init({
@@ -60,7 +60,7 @@ eruda.position(); // -> {x: 20, y: 20}
 Get tool, eg. console, elements panels.
 
 ```javascript
-var console = eruda.get('console');
+let console = eruda.get('console');
 console.log('eruda');
 ```
 
diff --git a/doc/README_CN.md b/doc/README_CN.md
index 2d09798..ea72bb6 100644
--- a/doc/README_CN.md
+++ b/doc/README_CN.md
@@ -80,7 +80,7 @@ Js文件对于移动端来说略重（gzip后大概100kb）。建议通过url参
 * tool：指定要初始化哪些面板，默认加载所有。
 
 ```javascript
-var el = document.createElement('div');
+let el = document.createElement('div');
 document.body.appendChild(el);
 
 eruda.init({
diff --git a/doc/TOOL_API.md b/doc/TOOL_API.md
index ea6cc24..c2df200 100644
--- a/doc/TOOL_API.md
+++ b/doc/TOOL_API.md
@@ -22,7 +22,7 @@ Display console logs. Implementation detail follows the [console api spec](https
 |maxLogNum          |string |Max log number                 |
 
 ```javascript
-var console = eruda.get('console');
+let console = eruda.get('console');
 console.config.set('catchGlobalErr', true);
 ```
 
@@ -33,7 +33,7 @@ All these methods can be used in the same way as window.console object.
 Note: When called, a corresponding event is triggered.
 
 ```javascript
-var console = eruda.get('console');
+let console = eruda.get('console');
 console.log('eruda is a console for %s.', 'mobile browsers');
 console.table([{test: 1}, {test: 2}, {test2: 3}], 'test');
 console.error(new Error('eruda'));
@@ -295,7 +295,7 @@ Add color to select a color.
 Add a separator.
 
 ```javascript
-var cfg = eruda.util.createCfg('test');
+let cfg = eruda.util.createCfg('test');
 
 cfg.set(eruda.util.defaults(cfg.get(), {
     testBool: true,
diff --git a/eustia/evalCss.js b/eustia/evalCss.js
index e951402..4ed6cc7 100644
--- a/eustia/evalCss.js
+++ b/eustia/evalCss.js
@@ -3,13 +3,13 @@
 
 _('toStr each filter')
 
-var styleList = [],
-  scale = 1
+let styleList = []
+let scale = 1
 
 function exports(css, container) {
   css = toStr(css)
 
-  for (var i = 0, len = styleList.length; i < len; i++) {
+  for (let i = 0, len = styleList.length; i < len; i++) {
     if (styleList[i].css === css) return
   }
 
diff --git a/eustia/getFileName.js b/eustia/getFileName.js
index 4e4a5aa..5dc4c2c 100644
--- a/eustia/getFileName.js
+++ b/eustia/getFileName.js
@@ -4,7 +4,7 @@
 _('last trim')
 
 function exports(url) {
-  var ret = last(url.split('/'))
+  let ret = last(url.split('/'))
 
   if (ret.indexOf('?') > -1) ret = trim(ret.split('?')[0])
 
diff --git a/eustia/isCrossOrig.js b/eustia/isCrossOrig.js
index f30e4fb..1b7c462 100644
--- a/eustia/isCrossOrig.js
+++ b/eustia/isCrossOrig.js
@@ -3,7 +3,7 @@
 
 _('startWith')
 
-var origin = window.location.origin
+let origin = window.location.origin
 
 function exports(url) {
   return !startWith(url, origin)
diff --git a/eustia/isErudaEl.js b/eustia/isErudaEl.js
index 330308a..66a96c4 100644
--- a/eustia/isErudaEl.js
+++ b/eustia/isErudaEl.js
@@ -2,7 +2,7 @@
  */
 
 function exports(el) {
-  var parentNode = el.parentNode
+  let parentNode = el.parentNode
 
   if (!parentNode) return false
 
diff --git a/eustia/safeStorage.js b/eustia/safeStorage.js
index 8032d1b..35855c0 100644
--- a/eustia/safeStorage.js
+++ b/eustia/safeStorage.js
@@ -6,7 +6,7 @@ _('isUndef memStorage')
 function exports(type, memReplacement) {
   if (isUndef(memReplacement)) memReplacement = true
 
-  var ret
+  let ret
 
   switch (type) {
     case 'local':
@@ -19,9 +19,9 @@ function exports(type, memReplacement) {
 
   try {
     // Safari private browsing
-    var x = 'test-localStorage-' + Date.now()
+    let x = 'test-localStorage-' + Date.now()
     ret.setItem(x, x)
-    var y = ret.getItem(x)
+    let y = ret.getItem(x)
     ret.removeItem(x)
     if (y !== x) throw new Error()
   } catch (e) {
diff --git a/karma.conf.js b/karma.conf.js
index 1ad7563..7fdf3e0 100644
--- a/karma.conf.js
+++ b/karma.conf.js
@@ -1,4 +1,4 @@
-var webpackCfg = require('./script/webpack.dev')
+const webpackCfg = require('./script/webpack.dev')
 webpackCfg.devtool = 'inline-source-map'
 
 module.exports = function(config) {
diff --git a/karma.sauce.js b/karma.sauce.js
index 7a2cd20..b9823fd 100644
--- a/karma.sauce.js
+++ b/karma.sauce.js
@@ -1,5 +1,5 @@
 module.exports = function(config) {
-  var customLaunchers = {
+  let customLaunchers = {
     sl_ios_safari_8: {
       base: 'SauceLabs',
       browserName: 'iphone',
diff --git a/script/coverage.js b/script/coverage.js
index da396b8..d1d2929 100644
--- a/script/coverage.js
+++ b/script/coverage.js
@@ -1,22 +1,22 @@
-var path = require('path'),
-  util = require('./util'),
-  istanbul = require('istanbul')
+const path = require('path')
+const util = require('./util')
+const istanbul = require('istanbul')
 
-var collector = new istanbul.Collector(),
-  reporter = new istanbul.Reporter()
+let collector = new istanbul.Collector()
+let reporter = new istanbul.Reporter()
 
-var remappedJson = require('../coverage/coverage-remapped.json')
+let remappedJson = require('../coverage/coverage-remapped.json')
 
-var coverage = util.reduce(
+let coverage = util.reduce(
   util.keys(remappedJson),
   function(result, source) {
     if (isSrc()) {
-      var correctPath = source.replace(
+      let correctPath = source.replace(
         path.resolve(__dirname, '../src'),
         path.resolve(__dirname, '../')
       )
 
-      var val = remappedJson[source]
+      let val = remappedJson[source]
       val.path = correctPath
       result[correctPath] = val
     }
diff --git a/script/cpTestLib.js b/script/cpTestLib.js
index b90a778..e243817 100644
--- a/script/cpTestLib.js
+++ b/script/cpTestLib.js
@@ -1,6 +1,6 @@
-var copy = require('copy'),
-  path = require('path'),
-  util = require('./util')
+const copy = require('copy')
+const path = require('path')
+const util = require('./util')
 
 util.mkdir(path.resolve(__dirname, '../test/lib'), function(err) {
   if (err) return console.log(err)
diff --git a/script/webpack.base.js b/script/webpack.base.js
index 2a40a0e..6be7ca4 100644
--- a/script/webpack.base.js
+++ b/script/webpack.base.js
@@ -1,15 +1,15 @@
-var autoprefixer = require('autoprefixer'),
-  classPrefix = require('postcss-class-prefix'),
-  webpack = require('webpack'),
-  pkg = require('../package.json'),
-  path = require('path')
+const autoprefixer = require('autoprefixer')
+const classPrefix = require('postcss-class-prefix')
+const webpack = require('webpack')
+const pkg = require('../package.json')
+const path = require('path')
 
 process.traceDeprecation = true
 
-var nodeModDir = path.resolve('./node_modules/') + '/',
-  banner = pkg.name + ' v' + pkg.version + ' ' + pkg.homepage
+let nodeModDir = path.resolve('./node_modules/') + '/'
+let banner = pkg.name + ' v' + pkg.version + ' ' + pkg.homepage
 
-var postcssLoader = {
+let postcssLoader = {
   loader: 'postcss-loader',
   options: {
     plugins: [classPrefix('eruda-'), autoprefixer]
diff --git a/script/webpack.dev.js b/script/webpack.dev.js
index b3098b9..9f8d4e4 100644
--- a/script/webpack.dev.js
+++ b/script/webpack.dev.js
@@ -1,4 +1,4 @@
-var webpack = require('webpack')
+const webpack = require('webpack')
 
 exports = require('./webpack.base')
 
diff --git a/script/webpack.release.js b/script/webpack.release.js
index e00eef1..c452fa6 100644
--- a/script/webpack.release.js
+++ b/script/webpack.release.js
@@ -1,4 +1,4 @@
-var webpack = require('webpack')
+const webpack = require('webpack')
 
 exports = require('./webpack.base')
 
diff --git a/src/Console/stringify.js b/src/Console/stringify.js
index 64852b8..e24a407 100644
--- a/src/Console/stringify.js
+++ b/src/Console/stringify.js
@@ -10,8 +10,8 @@ let callbacks = {},
 if (isWorkerSupported) {
   tryIt(function() {
     /* Some browsers like uc mobile doesn't destroy worker properly after refreshing.
-         * After a few times of visiting, it reaches the maximum number of workers per site. 
-         */
+     * After a few times of visiting, it reaches the maximum number of workers per site. 
+     */
     worker = new StringifyWorker()
     worker.onmessage = function(e) {
       let [id, result] = e.data
diff --git a/src/lib/stringify.js b/src/lib/stringify.js
index e16e664..7a2bad9 100644
--- a/src/lib/stringify.js
+++ b/src/lib/stringify.js
@@ -287,8 +287,8 @@ class Visitor {
   }
   visit(val) {
     /* Add 0 to distinguish stringify generated id from JsonViewer id.
-         * When used in web worker, they are not calling the same uniqId method, thus result may be repeated.
-         */
+     * When used in web worker, they are not calling the same uniqId method, thus result may be repeated.
+     */
     let id = uniqId('erudaJson0')
 
     this._visited.push({ id, val, abstract: {} })
diff --git a/test/boot.js b/test/boot.js
index 9607e66..da9c863 100644
--- a/test/boot.js
+++ b/test/boot.js
@@ -1,7 +1,7 @@
 function boot(name, cb) {
   // Need a little delay to make sure width and height of webpack dev server iframe are initialized.
   setTimeout(function() {
-    var options = {
+    let options = {
       useShadowDom: false
     }
     if (name) {
@@ -34,7 +34,7 @@ function boot(name, cb) {
 }
 
 function loadJs(src, cb) {
-  var script = document.createElement('script')
+  let script = document.createElement('script')
   script.src = src + '.js'
   script.onload = cb
   document.body.appendChild(script)
diff --git a/test/console.js b/test/console.js
index fb8680f..d141693 100644
--- a/test/console.js
+++ b/test/console.js
@@ -1,6 +1,6 @@
 describe('console', function() {
-  var tool = eruda.get('console'),
-    $tool = $('.eruda-console')
+  let tool = eruda.get('console')
+  let $tool = $('.eruda-console')
 
   beforeEach(function() {
     eruda.show('console')
@@ -8,7 +8,7 @@ describe('console', function() {
   })
 
   it('string', function() {
-    var text = '<span>This is a log</span>'
+    let text = '<span>This is a log</span>'
 
     tool.log(text)
     expect($tool.find('.eruda-log')).toContainText(text)
@@ -26,7 +26,7 @@ describe('console', function() {
   })
 
   it('basic object', function() {
-    var obj = { a: 1 }
+    let obj = { a: 1 }
 
     tool.log(obj)
     expect($tool.find('.eruda-log')).toContainText('Object { a: 1 }')
@@ -97,8 +97,8 @@ describe('console', function() {
     })
 
     it('Repeat log', function() {
-      for (var i = 0; i < 10; i++) tool.log(1)
-      var $log = $tool.find('.eruda-log-item')
+      for (let i = 0; i < 10; i++) tool.log(1)
+      let $log = $tool.find('.eruda-log-item')
       expect($log).toHaveLength(1)
       expect($log.find('.eruda-count')).toContainText('10')
     })
@@ -136,7 +136,7 @@ describe('console', function() {
         return log.type !== 'error'
       })
 
-      var obj = {}
+      let obj = {}
       Object.defineProperty(obj, 'a', {
         get: function() {
           tool.error('deprecated')
@@ -191,11 +191,11 @@ describe('console', function() {
   })
 
   describe('config', function() {
-    var config = tool.config
+    let config = tool.config
 
     it('max number', function() {
       config.set('maxLogNum', '10')
-      for (var i = 0; i < 20; i++) tool.log(i)
+      for (let i = 0; i < 20; i++) tool.log(i)
       expect($tool.find('.eruda-log-item')).toHaveLength(10)
     })
 
@@ -253,7 +253,7 @@ describe('console', function() {
 
   describe('events', function() {
     it('log', function() {
-      var sum = 0
+      let sum = 0
       function add(num) {
         sum += num
       }
diff --git a/test/elements.js b/test/elements.js
index 4410c5e..f658dac 100644
--- a/test/elements.js
+++ b/test/elements.js
@@ -1,6 +1,6 @@
 describe('elements', function() {
-  var tool = eruda.get('elements'),
-    $tool = $('.eruda-elements')
+  let tool = eruda.get('elements')
+  let $tool = $('.eruda-elements')
 
   beforeEach(function() {
     eruda.show('elements')
diff --git a/test/eruda.js b/test/eruda.js
index 384ee34..c214afa 100644
--- a/test/eruda.js
+++ b/test/eruda.js
@@ -7,7 +7,7 @@ describe('devTools', function() {
     })
 
     it('init', function() {
-      var container = document.createElement('div')
+      let container = document.createElement('div')
       container.id = 'eruda'
       document.body.appendChild(container)
 
@@ -17,7 +17,7 @@ describe('devTools', function() {
         useShadowDom: false
       })
 
-      var $eruda = $('#eruda')
+      let $eruda = $('#eruda')
       expect($eruda.find('.eruda-dev-tools')).toHaveLength(1)
     })
   })
@@ -36,7 +36,7 @@ describe('devTools', function() {
     })
 
     it('show', function() {
-      var $tool = $('.eruda-test')
+      let $tool = $('.eruda-test')
       expect($tool).toBeHidden()
       eruda.show('test')
       expect($tool).toHaveCss({ display: 'block' })
diff --git a/test/index.html b/test/index.html
index 20a4a63..278bc1a 100644
--- a/test/index.html
+++ b/test/index.html
@@ -45,7 +45,7 @@
 </nav>
 <script>
     (function () {
-        var el = document.createElement('div');
+        let el = document.createElement('div');
         document.body.appendChild(el);
         setTimeout(function () {
             try 
diff --git a/test/info.js b/test/info.js
index 9a3b02a..5b09070 100644
--- a/test/info.js
+++ b/test/info.js
@@ -1,6 +1,6 @@
 describe('info', function() {
-  var tool = eruda.get('info'),
-    $tool = $('.eruda-info')
+  let tool = eruda.get('info')
+  let $tool = $('.eruda-info')
 
   describe('default', function() {
     it('location', function() {
diff --git a/test/manual.html b/test/manual.html
index 13ae25b..3b7e168 100644
--- a/test/manual.html
+++ b/test/manual.html
@@ -49,13 +49,13 @@
     }
     addClickEvent('issue17', function ()
     {
-        var B = function () {};
-        var A = function () { this._data = 'eruda' };
+        let B = function () {};
+        let A = function () { this._data = 'eruda' };
         A.prototype = Object.create(B.prototype);
         Object.defineProperty(A.prototype, 'data', {
             get: function () { return this._data }
         });
-        var a = new A();
+        let a = new A();
         console.log(a);
     });
     addClickEvent('plugin', function ()
@@ -72,7 +72,7 @@
                 }
             };
         });
-        var Tool = eruda.Tool;
+        let Tool = eruda.Tool;
         eruda.add(new (Tool.extend({
             name: 'test3',
             init: function ($el) 
@@ -89,7 +89,7 @@
             resolve();
         }).then(function (res)
         {
-            var a = res.a;
+            let a = res.a;
         })
     });
     addClickEvent('issue31', function () 
@@ -106,8 +106,8 @@
     });
     addClickEvent('big-array', function () 
     {
-        var arr = [];
-        for (var i = 0; i < 10000; i++) {
+        let arr = [];
+        for (let i = 0; i < 10000; i++) {
             arr.push(i);
         }
         console.log(arr);
diff --git a/test/network.js b/test/network.js
index 5c8b9cb..a2f9de6 100644
--- a/test/network.js
+++ b/test/network.js
@@ -1,7 +1,4 @@
 describe('network', function() {
-  var tool = eruda.get('network'),
-    $tool = $('.eruda-network')
-
   beforeEach(function() {
     eruda.show('network')
   })
diff --git a/test/resources.js b/test/resources.js
index 0a9e533..c749135 100644
--- a/test/resources.js
+++ b/test/resources.js
@@ -1,6 +1,5 @@
 describe('resources', function() {
-  var tool = eruda.get('resources'),
-    $tool = $('.eruda-resources')
+  let $tool = $('.eruda-resources')
 
   beforeEach(function() {
     eruda.show('resources')
diff --git a/test/settings.js b/test/settings.js
index d8d603e..c7cc628 100644
--- a/test/settings.js
+++ b/test/settings.js
@@ -1,8 +1,8 @@
 describe('settings', function() {
-  var tool = eruda.get('settings'),
-    $tool = $('.eruda-settings')
+  let tool = eruda.get('settings')
+  let $tool = $('.eruda-settings')
 
-  var cfg = eruda.config.create('eruda-test')
+  let cfg = eruda.config.create('eruda-test')
   cfg.set({
     testSwitch: false,
     testSelect: '1',
@@ -15,7 +15,7 @@ describe('settings', function() {
   })
 
   it('switch', function() {
-    var text = 'Test Switch'
+    let text = 'Test Switch'
 
     tool.switch(cfg, 'testSwitch', text)
     expect($tool.find('.eruda-switch')).toContainText(text)
@@ -29,10 +29,10 @@ describe('settings', function() {
   })
 
   it('select', function() {
-    var text = 'Test Select'
+    let text = 'Test Select'
 
     tool.select(cfg, 'testSelect', text, ['1', '2', '3'])
-    var $el = $tool.find('.eruda-select')
+    let $el = $tool.find('.eruda-select')
     expect($el.find('ul li').length).toEqual(3)
     expect($el.find('.eruda-head')).toContainText(text)
     expect($el.find('.eruda-val')).toContainText('1')
@@ -44,20 +44,20 @@ describe('settings', function() {
     expect(cfg.get('testSelect')).toBe('2')
   })
   it('range', function() {
-    var text = 'Test Range'
+    let text = 'Test Range'
 
     tool.range(cfg, 'testRange', text, { min: 0, max: 1, step: 0.1 })
-    var $el = $tool.find('.eruda-range')
+    let $el = $tool.find('.eruda-range')
     expect($el.find('.eruda-head')).toContainText(text)
     expect($el.find('input').length).toEqual(1)
     $el.find('.eruda-head').click()
   })
 
   it('color', function() {
-    var text = 'Test Color'
+    let text = 'Test Color'
 
     tool.color(cfg, 'testColor', text, ['#000', '#fff'])
-    var $el = $tool.find('.eruda-color')
+    let $el = $tool.find('.eruda-color')
     expect($el.find('.eruda-head')).toContainText(text)
     expect($el.find('ul li').length).toEqual(2)
     $el.find('.eruda-head').click()
diff --git a/test/snippets.js b/test/snippets.js
index c3bf1c5..da226d9 100644
--- a/test/snippets.js
+++ b/test/snippets.js
@@ -1,13 +1,13 @@
 describe('snippets', function() {
-  var tool = eruda.get('snippets'),
-    $tool = $('.eruda-snippets')
+  let tool = eruda.get('snippets')
+  let $tool = $('.eruda-snippets')
 
   describe('default', function() {
     it('border all', function() {
       expect($tool.find('.eruda-name').eq(0)).toContainText('Border All')
 
-      var $body = $('body'),
-        $btn = $tool.find('.eruda-run').eq(0)
+      let $body = $('body')
+      let $btn = $tool.find('.eruda-run').eq(0)
 
       $btn.click()
       expect($body).toHaveCss({ outlineWidth: '2px' })
@@ -26,8 +26,8 @@ describe('snippets', function() {
     it('edit page', function() {
       expect($tool.find('.eruda-name').eq(3)).toContainText('Edit Page')
 
-      var $body = $('body'),
-        $btn = $tool.find('.eruda-run').eq(3)
+      let $body = $('body')
+      let $btn = $tool.find('.eruda-run').eq(3)
 
       $btn.click()
       expect($body).toHaveAttr('contenteditable', 'true')
diff --git a/test/sources.js b/test/sources.js
index 73d418c..0e3fcd2 100644
--- a/test/sources.js
+++ b/test/sources.js
@@ -1,6 +1,6 @@
 describe('sources', function() {
-  var tool = eruda.get('sources'),
-    $tool = $('.eruda-sources')
+  let tool = eruda.get('sources')
+  let $tool = $('.eruda-sources')
 
   beforeEach(function() {
     eruda.show('sources')