ECMAScript6（ECMAScript 2015 ，ES5，ES2016）技术已经在前端圈子很流行了，他给前端开发人员带来了很多惊喜，提供的语法糖使复杂的操作变得简单。
本文没有详细描述这些新特性，因为网上都已经有很多相关的介绍了。主要针对ES6 新特性收集了相关范例代码，他可以让你快速了解这个新的javascript规范。
function() 函数的简写表示法，但它不绑定 this。
var odds = evens.map(v => v + 1); // no parentes and no bracketsvar nums = evens.map((v, i) => v + i);var pairs = evens.map(v => ({even: v, odd: v + 1}));// Statement bodiesnums.forEach(v => { if (v % 5 === 0) fives.push(v);});this 是如何工作的？
var object = { name: "Name", arrowGetName: () => this.name, regularGetName: function() { return this.name }, arrowGetThis: () => this, regularGetThis: function() { return this }}console.log(this.name)console.log(object.arrowGetName());console.log(object.arrowGetThis());console.log(this)console.log(object.regularGetName());console.log(object.regularGetThis());结果：
this.name -> object.arrowGetName() -> object.arrowGetThis() -> [object Window]this -> [object Window]object.regularGetName() -> Nameobject.regularGetThis() -> {"name":"Name"}我们知道“真正”语言中的类(Classes)。在 ES6 中类(Classes)其实是原型继承的语法糖。
class SkinnedMesh extends THREE.Mesh { constructor(geometry, materials) { super(geometry, materials); this.idMatrix = SkinnedMesh.defaultMatrix(); this.bones = []; this.boneMatrices = []; //... } update(camera) { //... super.update(); } get boneCount() { return this.bones.length; } set matrixType(matrixType) { this.idMatrix = SkinnedMesh[matrixType](); } static defaultMatrix() { return new THREE.Matrix4(); }}var theProtoObj = { toString: function() { return "The ProtoOBject To string" }}var handler = () => "handler"var obj = { // __proto__ __proto__: theProtoObj, // Shorthand for ‘handler: handler' handler, // Methods toString() { // Super calls return "d " + super.toString(); }, // Computed (dynamic) property names [ "prop_" + (() => 42)() ]: 42};console.log(obj.handler)console.log(obj.handler())console.log(obj.toString())console.log(obj.prop_42)结果：
obj.handler -> () => "handler"obj.handler() -> handlerobj.toString() -> d The ProtoOBject To stringobj.prop_42 -> 42
字符串插值的好语法
var name = "Bob", time = "today";var multiLine = `ThisLineSpans MultipleLines`console.log(`Hello ${name},how are you ${time}?`)console.log(multiLine)结果：
`Hello ${name},how are you ${time}?` -> Hello Bob,how are you today?multiLine -> This Line Spans Multiple Lines愚人码头注：列表匹配
// list "matching"var [a, , b] = [1,2,3];console.log(a)console.log(b)
结果：
a -> 1b -> 3
对象也能很好的解构
nodes = () => { return {op: "a", lhs: "b", rhs: "c"}}var { op: a, lhs: b , rhs: c } = nodes()console.log(a)console.log(b)console.log(c)结果：
a -> ab -> bc -> c
使用速记表示法。
nodes = () => { return {lhs: "a", op: "b", rhs: "c"}}// binds `op`, `lhs` and `rhs` in scopevar {op, lhs, rhs} = nodes()console.log(op)console.log(lhs)console.log(rhs)结果：
op -> blhs -> arhs -> c
可在参数位置使用
function g({name: x}) { return x}function m({name}) { return name}console.log(g({name: 5}))console.log(m({name: 5}))结果：
g({name: 5}) -> 5m({name: 5}) -> 5var [a] = []var [b = 1] = []var c = [];console.log(a)console.log(b);console.log(c);
结果：
a -> undefinedb -> 1c -> []
function f(x, y=12) { return x + y;}console.log(f(3))console.log(f(3,2))结果：
f(3) -> 15f(3,2) -> 5
在函数中：
function f(x, y, z) { return x + y + z;}// 传递数组的每个元素作为参数console.log(f(...[1,2,3]))结果：
f(...[1,2,3]) -> 6
在数组中：
var parts = ["shoulders", "knees"];var lyrics = ["head", ...parts, "and", "toes"]; console.log(lyrics)
结果：
lyrics -> ["head","shoulders","knees","and","toes"]
我们可以使用这个创造很酷的对象。
let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };console.log(x); // 1console.log(y); // 2console.log(z); // { a: 3, b: 4 }// Spread propertieslet n = { x, y, ...z };console.log(n); // { x: 1, y: 2, a: 3, b: 4 }console.log(obj)可惜的是它还不支持：
npm install --save-dev babel-plugin-transform-object-rest-spread
我们可以使用 rest 操作符来允许无限参数。
function demo(part1, ...part2) { return {part1, part2}}console.log(demo(1,2,3,4,5,6))结果：
demo(1,2,3,4,5,6) -> {"part1":1,"part2":[2,3,4,5,6]}let是新的var。 因为它有块级作用域。
{ var globalVar = "from demo1"}{ let globalLet = "from demo2";}console.log(globalVar)console.log(globalLet)结果：
globalVar -> from demo1globalLet -> ReferenceError: globalLet is not defined
但是，它不会向window分配任何内容：
let me = "go"; // 全局作用域var i = "able"; // 全局作用域console.log(window.me); console.log(window.i);
结果：
window.me -> undefinedwindow.i -> able
不能使用let重新声明一个变量：
let me = "foo";let me = "bar"; console.log(me);
结果：
SyntaxError: Identifier 'me' has already been declared
var me = "foo";var me = "bar"; console.log(me)
结果：
me -> bar
const 是只读变量。
const a = "b"a = "a"
结果：
TypeError: Assignment to constant variable.
应该注意，const 对象仍然可以被改变的。
const a = { a: "a" }a.a = "b"console.log(a)结果：
a -> {"a":"b"}迭代器的新类型，可以替代for..in。 它返回的是值而不是keys。
let list = [4, 5, 6];console.log(list)for (let i in list) { console.log(i);}结果：
list -> [4,5,6]i -> 0i -> 1i -> 2
let list = [4, 5, 6];console.log(list)for (let i of list) { console.log(i); }结果：
list -> [4,5,6]i -> 4i -> 5i -> 6
迭代器是一个比数组更动态的类型。
let infinite = { [Symbol.iterator]() { let c = 0; return { next() { c++; return { done: false, value: c } } } }}console.log("start");for (var n of infinite) { // truncate the sequence at 1000 if (n > 10) break; console.log(n);}结果：
"start" -> startn -> 1n -> 2n -> 3n -> 4n -> 5n -> 6n -> 7n -> 8n -> 9n -> 10
使用Typescript，我们可以看到它接口的样子：
interface IteratorResult { done: boolean; value: any;}interface Iterator { next(): IteratorResult;}interface Iterable { [Symbol.iterator](): Iterator}生成器创建迭代器，并且比迭代器更具动态性。他们不必以相同的方式跟踪状态 并不支持 done 的概念。
var infinity = { [Symbol.iterator]: function*() { var c = 1; for (;;) { yield c++; } }}console.log("start")for (var n of infinity) { // truncate the sequence at 1000 if (n > 10) break; console.log(n);}结果：
"start" -> startn -> 1n -> 2n -> 3n -> 4n -> 5n -> 6n -> 7n -> 8n -> 9n -> 10
使用Typescript 再次显示接口：
interface Generator extends Iterator { next(value?: any): IteratorResult; throw(exception: any);}function* Iterators and generator
一个产量的例子*
function* anotherGenerator(i) { yield i + 1; yield i + 2; yield i + 3;}function* generator(i) { yield i; yield* anotherGenerator(i); yield i + 10;}var gen = generator(10);console.log(gen.next().value); console.log(gen.next().value); console.log(gen.next().value); console.log(gen.next().value); console.log(gen.next().value);结果：
gen.next().value -> 10gen.next().value -> 11gen.next().value -> 12gen.next().value -> 13gen.next().value -> 20
ES6 为Unicode 提供了更好的支持。
var regex = new RegExp('/u{61}', 'u');console.log(regex.unicode)console.log("/uD842/uDFD7")console.log("/uD842/uDFD7".codePointAt())结果：
regex.unicode -> true"" -> "".codePointAt() -> 134103
原生支持模块。
import defaultMember from "module-name";import * as name from "module-name";import { member } from "module-name";import { member as alias } from "module-name";import { member1 , member2 } from "module-name";import { member1 , member2 as alias2 , [...] } from "module-name";import defaultMember, { member [ , [...] ] } from "module-name";import defaultMember, * as name from "module-name";import "module-name";export { name1, name2, …, nameN };export { variable1 as name1, variable2 as name2, …, nameN };export let name1, name2, …, nameN; // also varexport let name1 = …, name2 = …, …, nameN; // also var, constexport expression;export default expression;export default function (…) { … } // also class, function*export default function name1(…) { … } // also class, function*export { name1 as default, … };export * from …;export { name1, name2, …, nameN } from …;export { import1 as name1, import2 as name2, …, nameN } from …;Set 为数学对应，其中所有项目都是唯一的。对于知道SQL的人来说，这相当于distinct。
var set = new Set();set.add("Potato").add("Tomato").add("Tomato");console.log(set.size)console.log(set.has("Tomato"))for(var item of set) { console.log(item)}结果：
set.size -> 2set.has("Tomato") -> trueitem -> Potatoitem -> TomatoWeakSet对象允许您在集合中存储弱持有的对象。没有引用的对象将被垃圾回收。
var item = { a:"Potato"}var set = new WeakSet();set.add({ a:"Potato"}).add(item).add({ a:"Tomato"}).add({ a:"Tomato"});console.log(set.size)console.log(set.has({a:"Tomato"}))console.log(set.has(item))for(let item of set) { console.log(item)}结果：
set.size -> undefinedset.has({a:"Tomato"}) -> falseset.has(item) -> trueTypeError: set[Symbol.iterator] is not a functionMap 也称为词典。
var map = new Map();map.set("Potato", 12);map.set("Tomato", 34);console.log(map.get("Potato"))for(let item of map) { console.log(item)}for(let item in map) { console.log(item)}结果：
map.get("Potato") -> 12item -> ["Potato",12]item -> ["Tomato",34]可以使用除字符串之外的其他类型。
var map = new Map();var key = {a: "a"}map.set(key, 12);console.log(map.get(key))console.log(map.get({a: "a"}))结果：
map.get(key) -> 12map.get({a: "a"}) -> undefined使用键的对象，并且只保留对键的弱引用。
var wm = new WeakMap();var o1 = {}var o2 = {}var o3 = {}wm.set(o1, 1);wm.set(o2, 2);wm.set(o3, {a: "a"});wm.set({}, 4);console.log(wm.get(o2));console.log(wm.has({}))delete o2;console.log(wm.get(o3));for(let item in wm) { console.log(item)}for(let item of wm) { console.log(item)}结果：
wm.get(o2) -> 2wm.has({}) -> falsewm.get(o3) -> {"a":"a"}TypeError: wm[Symbol.iterator] is not a function代理可以用来改变对象的行为。 它们允许我们定义 trap 。
var obj = function ProfanityGenerator() { return { words: "Horrible words" }}()var handler = function CensoringHandler() { return { get: function (target, key) { return target[key].replace("Horrible", "Nice"); }, }}()var proxy = new Proxy(obj, handler);console.log(proxy.words);结果：
proxy.words -> Nice words
提供以下 trap ：
var handler ={ get:..., set:..., has:..., deleteProperty:..., apply:..., construct:..., getOwnPropertyDescriptor:..., defineProperty:..., getPrototypeOf:..., setPrototypeOf:..., enumerate:..., ownKeys:..., preventExtensions:..., isExtensible:...}Symbols 是一个新类型。 可用于创建匿名属性。
var typeSymbol = Symbol("type");class Pet { constructor(type) { this[typeSymbol] = type; } getType() { return this[typeSymbol]; }}var a = new Pet("dog");console.log(a.getType());console.log(Object.getOwnPropertyNames(a))console.log(Symbol("a") === Symbol("a"))结果：
a.getType() -> dogObject.getOwnPropertyNames(a) -> []Symbol("a") === Symbol("a") -> false我们现在可以继承原生类。
class CustomArray extends Array {}var a = new CustomArray();a[0] = 2console.log(a[0])结果：
a[0] -> 2
不能使用数组的代理(Proxy)来覆盖getter函数。
各种新的方法和常量。
console.log(Number.EPSILON)console.log(Number.isInteger(Infinity))console.log(Number.isNaN("NaN"))console.log(Math.acosh(3))console.log(Math.hypot(3, 4))console.log(Math.imul(Math.pow(2, 32) - 1, Math.pow(2, 32) - 2))console.log("abcde".includes("cd") )console.log("abc".repeat(3) )console.log(Array.of(1, 2, 3) )console.log([0, 0, 0].fill(7, 1) )console.log([1, 2, 3].find(x => x == 3) )console.log([1, 2, 3].findIndex(x => x == 2)) console.log([1, 2, 3, 4, 5].copyWithin(3, 0)) console.log(["a", "b", "c"].entries() )console.log(["a", "b", "c"].keys() )console.log(["a", "b", "c"].values() )console.log(Object.assign({}, { origin: new Point(0,0) }))结果：
Number.EPSILON -> 2.220446049250313e-16Number.isInteger(Infinity) -> falseNumber.isNaN("NaN") -> falseMath.acosh(3) -> 1.7627471740390859Math.hypot(3, 4) -> 5Math.imul(Math.pow(2, 32) - 1, Math.pow(2, 32) - 2) -> 2"abcde".includes("cd") -> true"abc".repeat(3) -> abcabcabcArray.of(1, 2, 3) -> [1,2,3][0, 0, 0].fill(7, 1) -> [0,7,7][1, 2, 3].find(x => x == 3) -> 3[1, 2, 3].findIndex(x => x == 2) -> 1[1, 2, 3, 4, 5].copyWithin(3, 0) -> [1,2,3,1,2]["a", "b", "c"].entries() -> {}["a", "b", "c"].keys() -> {}["a", "b", "c"].values() -> TypeError: ["a","b","c"].values is not a functionObject.assign({}, { origin: new Point(0,0) }) -> ReferenceError: Point is not defined文档: Number, Math, Array.from, Array.of, Array.prototype.copyWithin, Object.assign
二进制和八进制数字的字面量。
console.log(0b11111)console.log(0o2342)console.log(0xff); // also in es5
结果：
0b11111 -> 310o2342 -> 12500xff -> 255
异步编程。
var p1 = new Promise((resolve, reject) => { setTimeout(() => resolve("1"), 101)})var p2 = new Promise((resolve, reject) => { setTimeout(() => resolve("2"), 100)})Promise.race([p1, p2]).then((res) => { console.log(res)})Promise.all([p1, p2]).then((res) => { console.log(res)})结果：
res -> 2res -> ["1","2"]
var p1 = Promise.resolve("1")var p2 = Promise.reject("2")Promise.race([p1, p2]).then((res) => { console.log(res)})结果：
res -> 1
如果一个 promise 失败，all和race也将 reject(拒绝)。
var p1 = new Promise((resolve, reject) => { setTimeout(() => resolve("1"), 1001)})var p2 = new Promise((resolve, reject) => { setTimeout(() => reject("2"), 1)})Promise.race([p1, p2]).then((res) => { console.log("success" + res)}, res => { console.log("error " + res)})Promise.all([p1, p2]).then((res) => { console.log("success" + res)}, res => { console.log("error " + res)})结果：
"error " + res -> error 2"error " + res -> error 2
新类型的元编程与新的API现有的还有一些新的方法。
var z = {w: "Super Hello"}var y = {x: "hello", __proto__: z};console.log(Reflect.getOwnPropertyDescriptor(y, "x"));console.log(Reflect.has(y, "w"));console.log(Reflect.ownKeys(y, "w"));console.log(Reflect.has(y, "x"));console.log(Reflect.deleteProperty(y,"x"))console.log(Reflect.has(y, "x"));结果：
Reflect.getOwnPropertyDescriptor(y, "x") -> {"value":"hello","writable":true,"enumerable":true,"configurable":true}Reflect.has(y, "w") -> trueReflect.ownKeys(y, "w") -> ["x"]Reflect.has(y, "x") -> trueReflect.deleteProperty(y,"x") -> trueReflect.has(y, "x") -> false尾调用的概念非常简单，一句话就能说清楚，就是指某个函数的最后一步是调用另一个函数。
ES6可以确保尾调用不会造成堆栈溢出。 （不是所有的实现工作）。
function factorial(n, acc = 1) { if (n <= 1) return acc; return factorial(n - 1, n * acc);}console.log(factorial(10))console.log(factorial(100))console.log(factorial(1000))console.log(factorial(10000))console.log(factorial(100000))console.log(factorial(1000000))结果：
factorial(10) -> 3628800factorial(100) -> 9.332621544394418e+157factorial(1000) -> Infinityfactorial(10000) -> Infinityfactorial(100000) -> RangeError: Maximum call stack size exceededfactorial(1000000) -> RangeError: Maximum call stack size exceeded
原文：ES6 Features
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