Revision 1057518 of ECMAScript 6 support in Mozilla

<div>{{jsSidebar("New_in_JS")}}</div>

<p>ECMAScript 2015 (6th Edition) is the current version of the ECMAScript Language Specification standard. Commonly referred to as "ES6", it defines the standard for the <a href="/en-US/docs/Web/JavaScript">JavaScript</a> implementation in <a href="/en-US/docs/Mozilla/Projects/SpiderMonkey">SpiderMonkey</a>, the engine used in Firefox and other Mozilla applications.</p>

<p>Code-named "ES.next" or "Harmony", the first working draft (based on <a href="/en-US/docs/Web/JavaScript/New_in_JavaScript/ECMAScript_5_support_in_Mozilla">ECMAScript 5.1</a>) was published on July 12, 2011 as "ES.next". In August 2014, the ECMAScript 6 draft specification was feature frozen and went through a stabilization and bug fixing period. Finally, ECMA-262 Edition 6 got officially approved and published as a standard on June 17, 2015 by the ECMA General Assembly. It will also appear as the international industry standard ISO/IEC 16262:2016.</p>

<p>A <a href="https://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf">PDF</a> and <a href="https://www.ecma-international.org/ecma-262/6.0/index.html">HTML</a> version of the standard can be <a href="https://www.ecma-international.org/publications/standards/Ecma-262.htm">freely downloaded on ecma-international.org</a>.</p>

<p>A channel for feedback on ECMAScript standards is <a href="https://mail.mozilla.org/listinfo/es-discuss">es-discuss</a>.</p>

<h2 id="Already_supported_by_Firefox">Already supported by Firefox</h2>

<p>The features listed here are already supported in Firefox; the version in which support was added is also indicated for each feature.</p>

<h3 id="Standard_library">Standard library</h3>

<h4 id="Additions_to_the_Array_object">Additions to the <code>Array</code> object</h4>

<ul>
 <li>{{jsxref("Array")}} iteration with <code>for...of</code> (<a href="/en-US/Firefox/Releases/13">Firefox 13</a>)</li>
 <li>{{jsxref("Array.from()")}} (<a href="/en-US/Firefox/Releases/32">Firefox 32</a>)</li>
 <li>{{jsxref("Array.of()")}} (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
 <li>{{jsxref("Array.prototype.fill()")}} (<a href="/en-US/Firefox/Releases/31">Firefox 31</a>)</li>
 <li>{{jsxref("Array.prototype.find()")}}, {{jsxref("Array.prototype.findIndex()")}} (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
 <li>{{jsxref("Array.prototype.entries()")}},<br />
  {{jsxref("Array.prototype.keys()")}} (<a href="/en-US/Firefox/Releases/28">Firefox 28</a>)</li>
 <li>{{jsxref("Array.prototype.copyWithin()")}} (<a href="/en-US/Firefox/Releases/32">Firefox 32</a>)</li>
 <li>{{jsxref("Array.@@species", "get Array[@@species]")}} (<a href="/en-US/Firefox/Releases/48">Firefox 48</a>)</li>
</ul>

<h4 id="New_Map_and_Set_objects_and_their_weak_counterparts">New <code>Map</code> and <code>Set</code> objects, and their weak counterparts</h4>

<ul>
 <li>{{jsxref("Map")}} (<a href="/en-US/Firefox/Releases/13">Firefox 13</a>)

  <ul>
   <li>{{jsxref("Map")}} iteration with <code>for...of</code> (<a href="/en-US/Firefox/Releases/17">Firefox 17</a>)</li>
   <li>{{jsxref("Map.prototype.forEach()")}} (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
   <li>{{jsxref("Map.prototype.entries()")}},<br />
    {{jsxref("Map.prototype.keys()")}},<br />
    {{jsxref("Map.prototype.values()")}} (<a href="/en-US/Firefox/Releases/20">Firefox 20</a>)</li>
   <li>Constructor argument: <code>new {{jsxref("Map")}}(null)</code> (<a href="/en-US/Firefox/Releases/37">Firefox 37</a>)</li>
   <li>Monkey-patched <code>set()</code> in Constructor (<a href="/en-US/Firefox/Releases/37">Firefox 37</a>)</li>
   <li>{{jsxref("Map.@@species", "get Map[@@species]")}} (<a href="/en-US/Firefox/Releases/41">Firefox 41</a>)</li>
  </ul>
 </li>
 <li>{{jsxref("Set")}} (<a href="/en-US/Firefox/Releases/13">Firefox 13</a>)
  <ul>
   <li>{{jsxref("Set")}} iteration with <code>for...of</code> (<a href="/en-US/Firefox/Releases/17">Firefox 17</a>)</li>
   <li>{{jsxref("Set.prototype.forEach()")}} (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
   <li>{{jsxref("Set.prototype.entries()")}},<br />
    {{jsxref("Set.prototype.keys()")}},<br />
    {{jsxref("Set.prototype.values()")}} (<a href="/en-US/Firefox/Releases/24">Firefox 24</a>)</li>
   <li>Constructor argument: <code>new {{jsxref("Set")}}(null)</code> (<a href="/en-US/Firefox/Releases/37">Firefox 37</a>)</li>
   <li>Monkey-patched <code>add()</code> in Constructor (<a href="/en-US/Firefox/Releases/37">Firefox 37</a>)</li>
   <li>{{jsxref("Set.@@species", "get Set[@@species]")}} (<a href="/en-US/Firefox/Releases/41">Firefox 41</a>)</li>
  </ul>
 </li>
 <li>{{jsxref("WeakMap")}} (<a href="/en-US/Firefox/Releases/6">Firefox 6</a>)
  <ul>
   <li>{{jsxref("WeakMap.clear()")}} (<a href="/en-US/Firefox/Releases/20">Firefox 20</a>)</li>
   <li>optional iterable argument in {{jsxref("WeakMap")}} constructor (<a href="/en-US/Firefox/Releases/36">Firefox 36</a>)</li>
   <li>Constructor argument: <code>new {{jsxref("WeakMap")}}(null)</code> (<a href="/en-US/Firefox/Releases/37">Firefox 37</a>)</li>
   <li>Monkey-patched <code>set()</code> in Constructor (<a href="/en-US/Firefox/Releases/37">Firefox 37</a>)</li>
  </ul>
 </li>
 <li>{{jsxref("WeakSet")}} (<a href="/en-US/Firefox/Releases/34">Firefox 34</a>)
  <ul>
   <li>Constructor argument: <code>new {{jsxref("WeakSet")}}(null)</code> (<a href="/en-US/Firefox/Releases/37">Firefox 37</a>)</li>
   <li>Monkey-patched <code>add()</code> in Constructor (<a href="/en-US/Firefox/Releases/37">Firefox 37</a>)</li>
  </ul>
 </li>
</ul>

<h4 id="New_Math_functions">New <code>Math</code> functions</h4>

<ul>
 <li>{{jsxref("Math.imul()")}} (<a href="/en-US/Firefox/Releases/20">Firefox 20</a>)</li>
 <li>{{jsxref("Math.clz32()")}} (<a href="/en-US/Firefox/Releases/31">Firefox 31</a>)</li>
 <li>{{jsxref("Math.fround()")}} (<a href="/en-US/Firefox/Releases/26">Firefox 26</a>)</li>
 <li>{{jsxref("Math.log10()")}}, {{jsxref("Math.log2()")}}, {{jsxref("Math.log1p()")}}, {{jsxref("Math.expm1()")}}, {{jsxref("Math.cosh()")}}, {{jsxref("Math.sinh()")}}, {{jsxref("Math.tanh()")}}, {{jsxref("Math.acosh()")}}, {{jsxref("Math.asinh()")}}, {{jsxref("Math.atanh()")}}, {{jsxref("Math.hypot()")}}, {{jsxref("Math.trunc()")}}, {{jsxref("Math.sign()")}}, {{jsxref("Math.cbrt()")}} (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
</ul>

<h4 id="Additions_to_the_Number_object">Additions to the <code>Number</code> object</h4>

<ul>
 <li>{{jsxref("Number.isNaN()")}} (<a href="/en-US/Firefox/Releases/16">Firefox 16</a>)</li>
 <li>{{jsxref("Number.isFinite()")}} (<a href="/en-US/Firefox/Releases/16">Firefox 16</a>)</li>
 <li>{{jsxref("Number.isInteger()")}} (<a href="/en-US/Firefox/Releases/16">Firefox 16</a>)</li>
 <li>{{jsxref("Number.parseInt()")}} (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
 <li>{{jsxref("Number.parseFloat()")}} (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
 <li>{{jsxref("Number.EPSILON")}} (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
 <li>{{jsxref("Number.MAX_SAFE_INTEGER")}}, {{jsxref("Number.MIN_SAFE_INTEGER")}} (<a href="/en-US/Firefox/Releases/31">Firefox 31</a>)</li>
 <li>{{jsxref("Number.isSafeInteger()")}} (<a href="/en-US/Firefox/Releases/32">Firefox 32</a>)</li>
</ul>

<h4 id="Additions_to_the_Object_object">Additions to the <code>Object</code> object</h4>

<ul>
 <li>{{jsxref("Object.prototype.__proto__")}} has been standardized</li>
 <li>{{jsxref("Object.is()")}} (<a href="/en-US/Firefox/Releases/22">Firefox 22</a>)</li>
 <li>{{jsxref("Object.setPrototypeOf()")}} (<a href="/en-US/Firefox/Releases/31">Firefox 31</a>)</li>
 <li>{{jsxref("Object.assign()")}} (<a href="/en-US/Firefox/Releases/34">Firefox 34</a>)</li>
 <li>{{jsxref("Object.getOwnPropertySymbols()")}} (<a href="/en-US/Firefox/Releases/33">Firefox 33</a>)</li>
</ul>

<h4 id="Additions_to_the_Date_object">Additions to the <code>Date</code> object</h4>

<ul>
 <li>{{jsxref("Date.prototype")}} is an ordinary object (<a href="/en-US/Firefox/Releases/41">Firefox 41</a>)</li>
 <li>generic {{jsxref("Date.prototype.toString")}} (<a href="/en-US/Firefox/Releases/41">Firefox 41</a>)</li>
 <li>{{jsxref("Date.prototype.@@toPrimitive", "Date.prototype[@@toPrimitive]")}} (<a href="/en-US/Firefox/Releases/44">Firefox 44</a>)</li>
</ul>

<h4 id="New_Promise_object">New <code>Promise</code> object</h4>

<ul>
 <li>{{jsxref("Promise")}} (<a href="/en-US/Firefox/Releases/24">Firefox 24</a>, enabled by default in <a href="/en-US/Firefox/Releases/29">Firefox 29</a>)</li>
</ul>

<h4>New <code>Proxy</code> object</h4>

<ul>
 <li>{{jsxref("Proxy")}} (<a href="/en-US/Firefox/Releases/18">Firefox 18</a>)</li>
 <li>{{jsxref("Global_Objects/Proxy/handler/preventExtensions", "preventExtensions()")}} trap (<a href="/en-US/Firefox/Releases/22">Firefox 22</a>)</li>
 <li>{{jsxref("Global_Objects/Proxy/handler/isExtensible", "isExtensible()")}} trap (<a href="/en-US/Firefox/Releases/31">Firefox 31</a>)</li>
 <li>{{jsxref("Global_Objects/Proxy/handler/getPrototypeOf", "getPrototypeOf()")}} and&nbsp;{{jsxref("Global_Objects/Proxy/handler/setPrototypeOf", "setPrototypeOf()")}} traps (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
</ul>

<h4 id="New_Reflect_object">New <code>Reflect</code> object</h4>

<ul>
 <li>{{jsxref("Reflect")}} (<a href="/en-US/Firefox/Releases/42">Firefox 42</a>)</li>
</ul>

<h4 id="Additions_to_the_RegExp_object">Additions to the <code>RegExp</code> object</h4>

<ul>
 <li>{{jsxref("RegExp")}} sticky (y) flag (<a href="/en-US/Firefox/Releases/38">Firefox 38</a>)</li>
 <li>{{jsxref("RegExp")}} unicode (u) flag (<a href="/en-US/Firefox/Releases/46">Firefox 46</a>)</li>
 <li>generic {{jsxref("RegExp.prototype.toString")}} (<a href="/en-US/Firefox/Releases/39">Firefox 39</a>)</li>
 <li>{{jsxref("RegExp.prototype.@@match()", "RegExp.prototype[@@match]()")}} (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
 <li>{{jsxref("RegExp.prototype.@@replace()", "RegExp.prototype[@@replace]()")}} (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
 <li>{{jsxref("RegExp.prototype.@@search()", "RegExp.prototype[@@search]()")}} (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
 <li>{{jsxref("RegExp.prototype.@@split()", "RegExp.prototype[@@split]()")}} (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
 <li>{{jsxref("RegExp.@@species", "get RegExp[@@species]")}} (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
</ul>

<h4 id="Additions_to_the_String_object">Additions to the <code>String</code> object</h4>

<ul>
 <li>{{jsxref("String.fromCodePoint()")}} (<a href="/en-US/Firefox/Releases/29">Firefox 29</a>)</li>
 <li>{{jsxref("String.prototype.codePointAt()")}} (<a href="/en-US/Firefox/Releases/29">Firefox 29</a>)</li>
 <li>{{jsxref("String.prototype.startsWith()")}}, {{jsxref("String.prototype.endsWith()")}} (<a href="/en-US/Firefox/Releases/17">Firefox 17</a>)</li>
 <li>{{jsxref("String.prototype.includes()")}} (<a href="/en-US/Firefox/Releases/40">Firefox 40</a>) (formerly <code>String.prototype.contains()</code> (<a href="/en-US/Firefox/Releases/17">Firefox 17</a>))</li>
 <li>{{jsxref("String.prototype.repeat()")}} (<a href="/en-US/Firefox/Releases/24">Firefox 24</a>)</li>
 <li>{{jsxref("String.prototype.normalize()")}} (<a href="/en-US/Firefox/Releases/31">Firefox 31</a>)</li>
 <li>{{jsxref("String.raw()")}} (<a href="/en-US/Firefox/Releases/34">Firefox 34</a>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Unicode_code_point_escapes">\u{XXXXXX}</a> Unicode code point escapes (<a href="/en-US/Firefox/Releases/40">Firefox 40</a>)</li>
</ul>

<h4 id="New_Symbol_object">New <code>Symbol</code> object</h4>

<ul>
 <li>{{jsxref("Symbol")}} (<a href="/en-US/Firefox/Releases/36">Firefox 36</a>)</li>
 <li>{{jsxref("Symbol.iterator")}} (<a href="/en-US/Firefox/Releases/36">Firefox 36</a>)</li>
 <li>{{jsxref("Symbol.for()")}} - global Symbol registry (<a href="/en-US/Firefox/Releases/36">Firefox 36</a>)</li>
 <li>{{jsxref("Symbol.match")}} (<a href="/en-US/Firefox/Releases/40">Firefox 40</a>)</li>
 <li>{{jsxref("Symbol.species")}} (<a href="/en-US/Firefox/Releases/41">Firefox 41</a>)</li>
 <li>{{jsxref("Symbol.toPrimitive")}} (<a href="/en-US/Firefox/Releases/44">Firefox 44</a>)</li>
 <li>{{jsxref("Symbol.prototype.@@toPrimitive", "Symbol.prototype[@@toPrimitive]")}} (<a href="/en-US/Firefox/Releases/44">Firefox 44</a>)</li>
 <li>{{jsxref("Symbol.replace")}} (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
 <li>{{jsxref("Symbol.search")}} (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
 <li>{{jsxref("Symbol.split")}} (<a href="/en-US/Firefox/Releases/49">Firefox 49</a>)</li>
</ul>

<h4 id="Typed_Arrays">Typed Arrays</h4>

<p>Typed arrays are specified as part of ECMAScript 6 and no longer in <a href="https://www.khronos.org/registry/typedarray/specs/latest/">their own specification</a>.</p>

<ul>
 <li>{{jsxref("ArrayBuffer")}}</li>
 <li>{{jsxref("ArrayBuffer.@@species", "get ArrayBuffer[@@species]")}} (<a href="/en-US/Firefox/Releases/48">Firefox 48</a>)</li>
 <li>{{jsxref("DataView")}}</li>
 <li>{{jsxref("Int8Array")}}</li>
 <li>{{jsxref("Uint8Array")}}</li>
 <li>{{jsxref("Uint8ClampedArray")}}</li>
 <li>{{jsxref("Int16Array")}}</li>
 <li>{{jsxref("Uint16Array")}}</li>
 <li>{{jsxref("Int32Array")}}</li>
 <li>{{jsxref("Uint32Array")}}</li>
 <li>{{jsxref("Float32Array")}}</li>
 <li>{{jsxref("Float64Array")}}</li>
 <li>{{jsxref("TypedArray.@@species", "get %TypedArray%[@@species]")}} (<a href="/en-US/Firefox/Releases/48">Firefox 48</a>)</li>
</ul>

<h3 id="Expressions_and_operators">Expressions and operators</h3>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/new.target">new.target</a> (<a href="/en-US/Firefox/Releases/41">Firefox 41</a>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator">Spread operator for arrays</a> (<a href="/en-US/Firefox/Releases/16">Firefox 16</a>)
  <ul>
   <li>use <code>Symbol.iterator</code> property (<a href="/en-US/Firefox/Releases/36">Firefox 36</a>)</li>
  </ul>
 </li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator">Spread operator for function calls</a> (<a href="/en-US/Firefox/Releases/27">Firefox 27</a>)
  <ul>
   <li>use <code>Symbol.iterator</code> property (<a href="/en-US/Firefox/Releases/36">Firefox 36</a>)</li>
  </ul>
 </li>
</ul>

<h3 id="Statements">Statements</h3>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/for...of"><code>for...of</code></a> (<a href="/en-US/Firefox/Releases/13">Firefox 13</a>)

  <ul>
   <li>works in terms of <code>.iterator()</code> and <code>.next()</code> (<a href="/en-US/Firefox/Releases/17">Firefox 17</a>)</li>
   <li>use <code>"@@iterator"</code> property (<a href="/en-US/Firefox/Releases/27">Firefox 27</a>)</li>
   <li>use <code>Symbol.iterator</code> property (<a href="/en-US/Firefox/Releases/36">Firefox 36</a>)</li>
  </ul>
 </li>
</ul>

<h3 id="Functions">Functions</h3>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/rest_parameters">Rest parameters</a> (<a href="/en-US/Firefox/Releases/15">Firefox 15</a>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/default_parameters">Default parameters</a> (<a href="/en-US/Firefox/Releases/15">Firefox 15</a>)
  <ul>
   <li>Parameters without defaults after default parameters (<a href="/en-US/Firefox/Releases/26">Firefox 26</a>)</li>
   <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters#Destructured_parameter_with_default_value_assignment" title="Default function parameters allow formal parameters to be initialized with default values if no value or undefined is passed.">Destructured parameters with default value assignment</a> (<a href="/en-US/Firefox/Releases/41">Firefox 41</a>)</li>
  </ul>
 </li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/arrow_functions">Arrow functions</a> (<a href="/en-US/Firefox/Releases/22">Firefox 22</a>)</li>
 <li>{{jsxref("Statements/function*", "Generator function")}} (<a href="/en-US/Firefox/Releases/26">Firefox 26</a>)
  <ul>
   <li>{{jsxref("Operators/yield", "yield")}} (<a href="/en-US/Firefox/Releases/26">Firefox 26</a>)</li>
   <li>{{jsxref("Operators/yield*", "yield*")}} (<a href="/en-US/Firefox/Releases/27">Firefox 27</a>)</li>
  </ul>
 </li>
 <li>{{jsxref("Functions/arguments/@@iterator", "arguments[@@iterator]")}} (<a href="/en-US/Firefox/Releases/46">Firefox 46</a>)</li>
</ul>

<h3 id="Other_features">Other features</h3>

<ul>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Numeric_literals">Binary and octal numeric literals</a> (<a href="/en-US/Firefox/Releases/25">Firefox 25</a>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/template_strings">Template strings</a> (<a href="/en-US/Firefox/Releases/34">Firefox 34</a>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Property_definitions">Object initializer: shorthand property names</a> (<a href="/en-US/Firefox/Releases/33">Firefox 33</a>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Computed_property_names">Object initializer: computed property names</a> (<a href="/en-US/Firefox/Releases/34">Firefox 34</a>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Method_definitions">Object initializer: shorthand method names</a> (<a href="/en-US/Firefox/Releases/34">Firefox 34</a>)</li>
</ul>

<h2 id="Features_not_compliant_with_the_ES6_specification">Features not compliant with the ES6 specification</h2>

<p>The following features are (partially) implemented in Firefox, but are not compliant with the specification. There are a couple of possible reasons for this: Firefox's implementation is based on an older draft of the ES6 specification, or Firefox's current implementation is an experimental design added before a similar feature was added to the ES6 specification.</p>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators">Legacy iterators and generators</a> (<a href="/en-US/docs/Web/JavaScript/New_in_JavaScript/1.7">JS 1.7</a>, <a href="/en-US/Firefox/Releases/2">Firefox 2</a>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">Destructuring assignment</a> (<a href="/en-US/docs/Web/JavaScript/New_in_JavaScript/1.7">JS 1.7</a>, <a href="/en-US/Firefox/Releases/2">Firefox 2</a>) (ES6 compliance {{bug("950547")}})</li>
 <li>{{jsxref("Statements/const", "const")}} (<a href="/en-US/docs/Web/JavaScript/New_in_JavaScript/1.5">JS 1.5</a>, Firefox 1.0) (ES6 compliance {{bug("950547")}})</li>
 <li>{{jsxref("Statements/let", "let")}} (<a href="/en-US/docs/Web/JavaScript/New_in_JavaScript/1.7">JS 1.7</a>, <a href="/en-US/Firefox/Releases/2">Firefox 2</a>) (ES6 compliance {{bug("950547")}})</li>
</ul>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/New_in_JavaScript/ECMAScript_7_support_in_Mozilla">ECMAScript 7 support in Mozilla</a></li>
 <li><a href="https://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts">ECMAScript 6 specification drafts</a></li>
 <li><a href="https://bugzilla.mozilla.org/show_bug.cgi?id=694100">Mozilla ES6 tracking bug</a></li>
 <li><a href="https://kangax.github.io/compat-table/es6/" title="https://kangax.github.io/compat-table/es6/">ECMAScript 6 support across browsers</a></li>
</ul>