ECMAScript 6 Features 中文版

ECMAScript 6 Features 中文版

第一遍粗译,词不达意,欢迎提 issue


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Introduction 简介

ECMAScript 6 is the upcoming version of the ECMAScript standard. This standard is targeting ratification in June 2015. ES6 is a significant update to the language, and the first update to the language since ES5 was standardized in 2009. Implementation of these features in major JavaScript engines is underway now.

ECMAScript 6 是 ECMAScript 的下一代标准,预计将在 2015年6月 正式发布。ES6 的发布将是是这门语言自 2009 年 ES5 正式发布以来的首次更新,是一次富有意义的更新。Javascript核心引擎的新特性仍然在快速开发中。

See the draft ES6 standard for full specification of the ECMAScript 6 language.


ES6 includes the following new features:

ES6 的具体特性如下:

ECMAScript 6 Features 特性

Arrows 箭头函数

Arrows are a function shorthand using the => syntax. They are syntactically similar to the related feature in C#, Java 8 and CoffeeScript. They support both expression and statement bodies. Unlike functions, arrows share the same lexical this as their surrounding code.

箭头函数是形如=>的函数简写形式,在语法上与 C#、Java 8 和 CoffeScript 非常相似,它们同时支持表达式和语句体,与function定义的函数所不同的是,箭头函数在上下文中共享相同的关键字this

// Expression bodies
// 表达式
var odds = => v + 1);
var nums =, i) => v + i);
var pairs = => ({even: v, odd: v + 1}));
// Statement bodies
// 语句体
nums.forEach(v => {
if (v % 5 === 0)
// Lexical this
// this 关键字
var bob = {
_name: "Bob",
_friends: ["Amy", "Bob", "Cinne", "Dylan", "Ellen"],
printFriends() {
this._friends.forEach(f =>
console.log(this._name + " knows " + f));

Classes 类

ES6 classes are a simple sugar over the prototype-based OO pattern. Having a single convenient declarative form makes class patterns easier to use, and encourages interoperability. Classes support prototype-based inheritance, super calls, instance and static methods and constructors.

ES6 的类是基于原型的面向对象模式的一个简单的语法糖,它有一个便捷的声明形式,并鼓励互操作性,这使得类模式更容易使用。class定义的类支持基于原型的继承、SuperCalls、实例和静态方法以及构造函数。

class SkinnedMesh extends THREE.Mesh {
constructor(geometry, materials) {
super(geometry, materials);
this.idMatrix = SkinnedMesh.defaultMatrix();
this.bones = [];
this.boneMatrices = [];
update(camera) {
static defaultMatrix() {
return new THREE.Matrix4();

Enhanced Object Literals 增强的Object字面量

Object literals are extended to support setting the prototype at construction, shorthand for foo: foo assignments, defining methods, making super calls, and computing property names with expressions. Together, these also bring object literals and class declarations closer together, and let object-based design benefit from some of the same conveniences.

Object字面量被扩展以支持以下特性:在构建的时候设置原型、foo: foo的简写形式赋值、定义方法、调用Super Calls、计算表达式的属性名称等。这样就使得Object字面量和类的声明的联系更加紧密,使得基于对象的设计更加便利

var obj = {
// __proto__
__proto__: theProtoObj,
// Shorthand for ‘handler: handler’
// ‘handler: handler’ 的简写形式
// Methods
toString() {
// Super calls
return "d " + super.toString();
// Computed (dynamic) property names
// 动态计算属性名称
[ 'prop_' + (() => 42)() ]: 42

Template Strings 模板字符串

Template strings provide syntactic sugar for constructing strings. This is similar to string interpolation features in Perl, Python and more. Optionally, a tag can be added to allow the string construction to be customized, avoiding injection attacks or constructing higher level data structures from string contents.


// Basic literal string creation
// 基础字符串字面量的创建
`In JavaScript '\n' is a line-feed.`
// Multiline strings
// 多行字符串
`In JavaScript this is
not legal.`
// String interpolation
// 字符串插值
var name = "Bob", time = "today";
`Hello ${name}, how are you ${time}?`
// Construct an HTTP request prefix is used to interpret the replacements and construction
// 构造一个HTTP请求前缀用来解释替换和构造,大意就是可以构造一个通用的HTTP prefix并通过赋值生成最终的HTTP请求
Content-Type: application/json
X-Credentials: ${credentials}
{ "foo": ${foo},
"bar": ${bar}}`(myOnReadyStateChangeHandler);

Destructuring 解构

Destructuring allows binding using pattern matching, with support for matching arrays and objects. Destructuring is fail-soft, similar to standard object lookup foo["bar"], producing undefined values when not found.


// list matching
// 列表匹配
var [a, , b] = [1,2,3];
// object matching
// 对象匹配
var { op: a, lhs: { op: b }, rhs: c }
= getASTNode()
// object matching shorthand
// binds `op`, `lhs` and `rhs` in scope
// 对象匹配简写形式
var {op, lhs, rhs} = getASTNode()
// 上面作者给的示例看得云里雾里的,这里我再给出一个
function today() { return { d: 2, m: 3, y: 2015 }; }
var { m: month, y: year } = today(); // month = 3, year = 2015
// Can be used in parameter position
// 也可以作为参数使用
function g({name: x}) {
g({name: 5})
// Fail-soft destructuring
// 失效弱化解构,结果查询不到时定义为 undefined
var [a] = [];
a === undefined;
// Fail-soft destructuring with defaults
// 具备默认值的失效弱化解构
var [a = 1] = [];
a === 1;

Default + Rest + Spread 默认值+多余参数组合+参数伸展

Callee-evaluated default parameter values. Turn an array into consecutive arguments in a function call. Bind trailing parameters to an array. Rest replaces the need for arguments and addresses common cases more directly.


  1. 首先,参数可以指定默认值
  2. 其次,可以通过…运算符将尾随参数转换为一个数组
  3. 最后,同样通过…运算符将作为参数的数组拆解为相应参数变量


function f(x, y=12) {
// y is 12 if not passed (or passed as undefined)
return x + y;
f(3) == 15
function f(x, ...y) {
// y is an Array
return x * y.length;
f(3, "hello", true) == 6
function f(x, y, z) {
return x + y + z;
// Pass each elem of array as argument
f(...[1,2,3]) == 6

Let + Const 操作符

Block-scoped binding constructs. let is the new var. const is single-assignment. Static restrictions prevent use before assignment.

let 和 const 属于块级作用域的绑定构造,let 是新的 var,只在块级作用域内有效,const单赋值,声明的是块级作用域的常量,静态限制在赋值之前禁止使用

function f() {
let x;
// okay, block scoped name
const x = "sneaky";
// error, const
x = "foo";
// error, already declared in block
let x = "inner";

Iterators + For..Of 迭代器 + For..of 循环

Iterator objects enable custom iteration like CLR IEnumerable or Java Iterable. Generalize to custom iterator-based iteration with for..of. Don’t require realizing an array, enabling lazy design patterns like LINQ.

迭代器对象允许像 CLI IEnumerable.aspx) 或者 Java Iterable 一样自定义迭代器。将for..in转换为自定义的基于迭代器的形如for..of的迭代,不需要实现一个数组,支持像 LINQ 一样的惰性设计模式

let fibonacci = {
[Symbol.iterator]() {
let pre = 0, cur = 1;
return {
next() {
[pre, cur] = [cur, pre + cur];
return { done: false, value: cur }
for (var n of fibonacci) {
// truncate the sequence at 1000
if (n > 1000)

Iteration is based on these duck-typed interfaces (using TypeScript type syntax for exposition only):

迭代器基于这些鸭子类型的接口 (仅使用TypeScript 类型的句法阐述问题):

interface IteratorResult {
done: boolean;
value: any;
interface Iterator {
next(): IteratorResult;
interface Iterable {
[Symbol.iterator](): Iterator

Generators 生成器

Generators simplify iterator-authoring using function* and yield. A function declared as function* returns a Generator instance. Generators are subtypes of iterators which include additional next and throw. These enable values to flow back into the generator, so yield is an expression form which returns a value (or throws).

生成器通过使用function*yield简化迭代器的编写, 形如function*的函数声明返回一个生成器实例,生成器是迭代器的子类型,迭代器包括附加的nextthrow,这使得值可以回流到生成器中,yield是一个返回或抛出一个值的表达式形式 。

Note: Can also be used to enable ‘await’-like async programming, see also ES7 await proposal.

var fibonacci = {
[Symbol.iterator]: function*() {
var pre = 0, cur = 1;
for (;;) {
var temp = pre;
pre = cur;
cur += temp;
yield cur;
for (var n of fibonacci) {
// truncate the sequence at 1000
if (n > 1000)

The generator interface is (using TypeScript type syntax for exposition only):
生成器接口如下(仅使用TypeScript 类型的句法阐述问题):

interface Generator extends Iterator {
next(value?: any): IteratorResult;
throw(exception: any);

Unicode 统一码

Non-breaking additions to support full Unicode, including new Unicode literal form in strings and new RegExp u mode to handle code points, as well as new APIs to process strings at the 21bit code points level. These additions support building global apps in JavaScript.

Non-breaking additions to support full Unicode

这句看了半天不知道作者想要表达什么,我就查了下资料,有一种可能是: 增加不换行空格的特性以全面支持Unicode,还有一种可能是:渐进增强地、非破坏性地全面支持Unicode,也就是说,新加入的特性并不影响老的代码的使用。我个人比较倾向于第二种解读。@sumhat提示说第二种解读是正确的

(续)字符串支持新的Unicode文本形式,也增加了新的正则表达式修饰符u来处理代码点,同时,新的API可以在21bit代码点级别上处理字符串,增加这些支持后可以使用 Javascript 构建全球化的应用。

// same as ES5.1
// 与 ES5.1 相同