Mozilla对ECMAScript 6的支持

ECMAScript 2015 (6th Edition)是目前ECMAScript语言规范的标准。通常被称为"ES6"，在SpiderMonkey 中它规定了JavaScript的实现标准, SpiderMonkey是一个JavaScript引擎，被广泛在火狐浏览器等谋智的众多产品中。

Code-named "ES.next" or "Harmony", the first working draft (based on ECMAScript 5.1) 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.

A PDF and HTML version of the standard can be freely downloaded on ecma-international.org.

A channel for feedback on ECMAScript standards is es-discuss.

Firefox 已经支持的 ECMAScript 6 特性

这里列出的功能已经在Firefox中支持；the version in which support was added is also indicated for each feature.

标准库

Additions to the Array object

• Array iteration with for...of (Firefox 13)
• Array.from() (Firefox 32)
• Array.of() (Firefox 25)
• Array.prototype.fill() (Firefox 31)
• Array.prototype.find(), Array.prototype.findIndex() (Firefox 25)
• Array.prototype.entries(),
  Array.prototype.keys() (Firefox 28)
• Array.prototype.copyWithin() (Firefox 32)
• get Array[@@species] (Firefox 48)

新的 Map 和 Set，以及 WeakMap 和 WeakSet 对象

• Map (Firefox 13)
  • Map iteration with for...of (Firefox 17)
  • Map.prototype.forEach() (Firefox 25)
  • Map.prototype.entries(),
    Map.prototype.keys(),
    Map.prototype.values() (Firefox 20)
  • Constructor argument: new Map(null) (Firefox 37)
  • Monkey-patched set() in Constructor (Firefox 37)
  • get Map[@@species] (Firefox 41)
• Set (Firefox 13)
  • Set iteration with for...of (Firefox 17)
  • Set.prototype.forEach() (Firefox 25)
  • Set.prototype.entries(),
    Set.prototype.keys(),
    Set.prototype.values() (Firefox 24)
  • Constructor argument: new Set(null) (Firefox 37)
  • Monkey-patched add() in Constructor (Firefox 37)
  • get Set[@@species] (Firefox 41)
• WeakMap (Firefox 6)
  • WeakMap.clear() (Firefox 20)
  • optional iterable argument in WeakMap constructor (Firefox 36)
  • Constructor argument: new WeakMap(null) (Firefox 37)
  • Monkey-patched set() in Constructor (Firefox 37)
• WeakSet (Firefox 34)
  • Constructor argument: new WeakSet(null) (Firefox 37)
  • Monkey-patched add() in Constructor (Firefox 37)

新的 Math 方法

• Math.imul() (Firefox 20)
• Math.clz32() (Firefox 31)
• Math.fround() (Firefox 26)
• Math.log10(), Math.log2(), Math.log1p(), Math.expm1(), Math.cosh(), Math.sinh(), Math.tanh(), Math.acosh(), Math.asinh(), Math.atanh(), Math.hypot(), Math.trunc(), Math.sign(), Math.cbrt() (Firefox 25)

Number 对象的补充

• Number.isNaN() (Firefox 16)
• Number.isFinite() (Firefox 16)
• Number.isInteger() (Firefox 16)
• Number.parseInt() (Firefox 25)
• Number.parseFloat() (Firefox 25)
• Number.EPSILON (Firefox 25)
• Number.MAX_SAFE_INTEGER, Number.MIN_SAFE_INTEGER (Firefox 31)
• Number.isSafeInteger() (Firefox 32)

Object 对象的补充

• Object.prototype.__proto__ 已经被标准化
• Object.is() (Firefox 22)
• Object.setPrototypeOf() (Firefox 31)
• Object.assign() (Firefox 34)
• Object.getOwnPropertySymbols() (Firefox 33)

Date 对象的补充

• Date.prototype is an ordinary object (Firefox 41)
• generic Date.prototype.toString (Firefox 41)
• Date.prototype[@@toPrimitive] (Firefox 44)

新的 Promise 对象

• Promise (Firefox 24,  在 Firefox 29 中默认启用)

新的 Reflect 对象

• Reflect (Firefox 42)

RegExp 对象的补充

• RegExp sticky (y) flag (Firefox 38)
• RegExp unicode (u) flag (Firefox 46)
• generic RegExp.prototype.toString (Firefox 39)
• RegExp.prototype[@@match]() (Firefox 49)
• RegExp.prototype[@@replace]() (Firefox 49)
• RegExp.prototype[@@search]() (Firefox 49)
• RegExp.prototype[@@split]() (Firefox 49)
• get RegExp[@@species] (Firefox 49)

String 对象的补充

• String.fromCodePoint() (Firefox 29)
• String.prototype.codePointAt() (Firefox 29)
• String.prototype.startsWith(), String.prototype.endsWith() (Firefox 17)
• String.prototype.includes() (Firefox 40) (formerly String.prototype.contains() (Firefox 17))
• String.prototype.repeat() (Firefox 24)
• String.prototype.normalize() (Firefox 31)
• String.raw() (Firefox 34)
• \u{XXXXXX} Unicode code point escapes (Firefox 40)

新的 Symbol 对象

• Symbol (Firefox 36)
• Symbol.iterator (Firefox 36)
• Symbol.for() - global Symbol registry (Firefox 36)
• Symbol.match (Firefox 40)
• Symbol.species (Firefox 41)
• Symbol.toPrimitive (Firefox 44)
• Symbol.prototype[@@toPrimitive] (Firefox 44)
• Symbol.replace (Firefox 49)
• Symbol.search (Firefox 49)
• Symbol.split (Firefox 49)
• Symbol.hasInstance (Firefox 50)

Typed Arrays

Typed arrays are specified as part of ECMAScript 6 and no longer in their own specification.

• ArrayBuffer
• get ArrayBuffer[@@species] (Firefox 48)
• DataView
• Int8Array
• Uint8Array
• Uint8ClampedArray
• Int16Array
• Uint16Array
• Int32Array
• Uint32Array
• Float32Array
• Float64Array
• get %TypedArray%[@@species] (Firefox 48)

表达式和操作符

• new.target (Firefox 41)

• Spread operator for arrays (Firefox 16)
  • use Symbol.iterator property (Firefox 36)
• Spread operator for function calls (Firefox 27)
  • use Symbol.iterator property (Firefox 36)

语句

• for...of (Firefox 13)
  • works in terms of .iterator() and .next() (Firefox 17)
  • use "@@iterator" property (Firefox 27)
  • use Symbol.iterator property (Firefox 36)

函数

• Rest parameters (Firefox 15)
• Default parameters (Firefox 15)
  • Parameters without defaults after default parameters (Firefox 26)
  • Destructured parameters with default value assignment (Firefox 41)
• Arrow functions (Firefox 22)
• Generator function (Firefox 26)
  • yield (Firefox 26)
  • yield* (Firefox 27)
• arguments[@@iterator] (Firefox 46)

其他特性

• Binary and octal numeric literals (Firefox 25)
• Template strings (Firefox 34)
• Object initializer: shorthand property names (Firefox 33)
• Object initializer: computed property names (Firefox 34)
• Object initializer: shorthand method names (Firefox 34)

和ES6规范不兼容的特性

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.

• Legacy iterators and generators (JS 1.7, Firefox 2)
  • ES6 iterators and generators implemented in Firefox 26+
• Destructuring assignment (JS 1.7, Firefox 2) (ES6 compliance bug 950547)
• const (JS 1.5, Firefox 1.0) (ES6 compliance bug 950547)
• let (JS 1.7, Firefox 2) (ES6 compliance bug 950547)
• Proxy (Firefox 18) (ES6 compliance bug 978228)

Features partially supported by Firefox

These features, while part of ECMAScript 6, are only partially implemented in Firefox, and are only available in nightly builds.

New class syntax

• Basic support (bug 837314)
• extends support
• static method definitions

还未支持的 ECMAScript 6 的功能

以下是 Firefox 实现（部分）的功能，但不符合规范。有那么几个能解释这个的原因：这些功能的实现是基于 ES6 规范较早期的草案，或 Firefox 的当前实现是一个实验性的设计，在与这个设计类似的功能加入到 ES6 规范之前。

• Legacy iterators and generators (JS 1.7, Firefox 2)
• Destructuring assignment (JS 1.7, Firefox 2) (ES6 compliance bug 1055984)
• const (JS 1.5, Firefox 1.0) (ES6 compliance bug 950547 implemented in Firefox 51)
• let (JS 1.7, Firefox 2) (ES6 compliance bug 950547 implemented in Firefox 51)

相关链接

• ECMAScript 6规范草案
• Mozilla ES6 tracking bug
• 支持ECMAScript 6的浏览器