定義：<article id="wikiArticle" style="font-style: normal !important; display: block; margin: 0px; padding: 0px 0px 20px; border-width: 0px 0px 3px; border-top-style: initial; border-right-style: initial; border-left-style: initial; border-top-color: initial; border-right-color: initial; border-left-color: initial; border-image: initial; position: relative; border-bottom-style: solid; border-bottom-color: rgb(61, 126, 154);">

語法節(jié)

基礎(chǔ)語法節(jié)

(參數(shù)1, 參數(shù)2, …, 參數(shù)N) => { 函數(shù)聲明 }
(參數(shù)1, 參數(shù)2, …, 參數(shù)N) => 表達(dá)式（單一）
//相當(dāng)于：(參數(shù)1, 參數(shù)2, …, 參數(shù)N) =>{ return 表達(dá)式; }

// 當(dāng)只有一個(gè)參數(shù)時(shí)跑杭，圓括號是可選的：
(單一參數(shù)) => {函數(shù)聲明}
單一參數(shù) => {函數(shù)聲明}

// 沒有參數(shù)的函數(shù)應(yīng)該寫成一對圓括號狮荔。
() => {函數(shù)聲明}

高級語法節(jié)

//加括號的函數(shù)體返回對象字面表達(dá)式：
參數(shù)=> ({foo: bar})

//支持剩余參數(shù)和默認(rèn)參數(shù)
(參數(shù)1, 參數(shù)2, ...rest) => {函數(shù)聲明}
(參數(shù)1 = 默認(rèn)值1,參數(shù)2, …, 參數(shù)N = 默認(rèn)值N) => {函數(shù)聲明}

//同樣支持參數(shù)列表解構(gòu)
let f = ([a, b] = [1, 2], {x: c} = {x: a + b}) => a + b + c;
f();  // 6

描述節(jié)

參考 "ES6 In Depth: Arrow functions" on hacks.mozilla.org.

引入箭頭函數(shù)有兩個(gè)方面的作用：更簡短的函數(shù)并且不綁定this幕随。

更短的函數(shù)節(jié)

var materials = [
  'Hydrogen',
  'Helium',
  'Lithium',
  'Beryllium'
];

materials.map(function(material) { 
  return material.length; 
}); // [8, 6, 7, 9]

materials.map((material) => {
  return material.length;
}); // [8, 6, 7, 9]

materials.map(material => material.length); // [8, 6, 7, 9]

不綁定this節(jié)

在箭頭函數(shù)出現(xiàn)之前存捺，每個(gè)新定義的函數(shù)都有它自己的 [this](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)值（在構(gòu)造函數(shù)的情況下是一個(gè)新對象，在嚴(yán)格模式的函數(shù)調(diào)用中為 undefined行您，如果該函數(shù)被作為“對象方法”調(diào)用則為基礎(chǔ)對象等）。This被證明是令人厭煩的面向?qū)ο箫L(fēng)格的編程。

function Person() {
  // Person() 構(gòu)造函數(shù)定義 `this`作為它自己的實(shí)例.
  this.age = 0;

  setInterval(function growUp() {
    // 在非嚴(yán)格模式, growUp()函數(shù)定義 `this`作為全局對象, 
    // 與在 Person()構(gòu)造函數(shù)中定義的 `this`并不相同.
    this.age++;
  }, 1000);
}

var p = new Person();

在ECMAScript 3/5中缭受，通過將this值分配給封閉的變量，可以解決this問題该互。

function Person() {
  var that = this;
  that.age = 0;

  setInterval(function growUp() {
    //  回調(diào)引用的是`that`變量, 其值是預(yù)期的對象. 
    that.age++;
  }, 1000);
}

或者米者，可以創(chuàng)建綁定函數(shù)，以便將預(yù)先分配的this值傳遞到綁定的目標(biāo)函數(shù)（上述示例中的growUp()函數(shù)）宇智。

箭頭函數(shù)不會創(chuàng)建自己的this,它只會從自己的作用域鏈的上一層繼承this蔓搞。因此，在下面的代碼中随橘，傳遞給setInterval的函數(shù)內(nèi)的this與封閉函數(shù)中的this值相同：

function Person(){
  this.age = 0;

  setInterval(() => {
    this.age++; // |this| 正確地指向person 對象
  }, 1000);
}

var p = new Person();

與嚴(yán)格模式的關(guān)系

鑒于 this 是詞法層面上的喂分，嚴(yán)格模式中與 this 相關(guān)的規(guī)則都將被忽略。

function Person() {
  this.age = 0;
  var closure = "123"
  setInterval(function growUp() {
    this.age++;
    console.log(closure)
  }, 1000);
}

var p = new Person();

function PersonX() {
  'use strict'
  this.age = 0;
  var closure = "123"
  setInterval(()=>{
    this.age++;
    console.log(closure)
  }, 1000);
}

var px = new PersonX();

嚴(yán)格模式的其他規(guī)則依然不變.

通過 call 或 apply 調(diào)用

由于 箭頭函數(shù)沒有自己的this指針机蔗，通過 call()* 或* apply() 方法調(diào)用一個(gè)函數(shù)時(shí)蒲祈，只能傳遞參數(shù)（不能綁定this---譯者注），他們的第一個(gè)參數(shù)會被忽略萝嘁。（這種現(xiàn)象對于bind方法同樣成立---譯者注）

var adder = {
  base : 1,

  add : function(a) {
    var f = v => v + this.base;
    return f(a);
  },

  addThruCall: function(a) {
    var f = v => v + this.base;
    var b = {
      base : 2
    };

    return f.call(b, a);
  }
};

console.log(adder.add(1));         // 輸出 2
console.log(adder.addThruCall(1)); // 仍然輸出 2（而不是3 ——譯者注）

不綁定arguments節(jié)

箭頭函數(shù)不綁定Arguments 對象梆掸。因此，在本示例中牙言，arguments只是引用了封閉作用域內(nèi)的arguments：

var arguments = [1, 2, 3];
var arr = () => arguments[0];

arr(); // 1

function foo(n) {
  var f = () => arguments[0] + n; // 隱式綁定 foo 函數(shù)的 arguments 對象. arguments[0] 是 n
  return f();
}

foo(1); // 2

在大多數(shù)情況下酸钦，使用剩余參數(shù)是相較使用arguments對象的更好選擇。

function foo() { 
  var f = (...args) => args[0]; 
  return f(2); 
}

foo(1); 
// 2

像函數(shù)一樣使用箭頭函數(shù)節(jié)

如上所述咱枉，箭頭函數(shù)表達(dá)式對非方法函數(shù)是最合適的卑硫。讓我們看看當(dāng)我們試著把它們作為方法時(shí)發(fā)生了什么徒恋。

'use strict';
var obj = {
  i: 10,
  b: () => console.log(this.i, this),
  c: function() {
    console.log( this.i, this)
  }
}
obj.b(); 
// undefined
obj.c(); 
// 10, Object {...}

箭頭函數(shù)沒有定義this綁定。另一個(gè)涉及Object.defineProperty()的示例：

'use strict';
var obj = {
  a: 10
};

Object.defineProperty(obj, "b", {
  get: () => {
    console.log(this.a, typeof this.a, this);
    return this.a+10; 
   // 代表全局對象 'Window', 因此 'this.a' 返回 'undefined'
  }
});

使用 new 操作符節(jié)

箭頭函數(shù)不能用作構(gòu)造器拔恰，和 new一起用會拋出錯(cuò)誤因谎。

var Foo = () => {};
var foo = new Foo(); // TypeError: Foo is not a constructor

使用prototype屬性節(jié)

箭頭函數(shù)沒有prototype屬性。

var Foo = () => {};
console.log(Foo.prototype); // undefined

使用 yield 關(guān)鍵字節(jié)

[yield](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/yield) 關(guān)鍵字通常不能在箭頭函數(shù)中使用（除非是嵌套在允許使用的函數(shù)內(nèi)）颜懊。因此财岔，箭頭函數(shù)不能用作生成器。

函數(shù)體節(jié)

箭頭函數(shù)可以有一個(gè)“簡寫體”或常見的“塊體”河爹。

在一個(gè)簡寫體中匠璧，只需要一個(gè)表達(dá)式，并附加一個(gè)隱式的返回值咸这。在塊體中夷恍，必須使用明確的return語句。

var func = x => x * x;                  
// 簡寫函數(shù) 省略return

var func = (x, y) => { return x + y; }; 
//常規(guī)編寫 明確的返回值

返回對象字面量節(jié)

記住用params => {object:literal}這種簡單的語法返回對象字面量是行不通的媳维。

var func = () => { foo: 1 };               
// Calling func() returns undefined!

var func = () => { foo: function() {} };   
// SyntaxError: function statement requires a name

這是因?yàn)榛ɡㄌ枺?code>{} ）里面的代碼被解析為一系列語句（即 foo 被認(rèn)為是一個(gè)標(biāo)簽酿雪，而非對象字面量的組成部分）。

所以侄刽，記得用圓括號把對象字面量包起來：

var func = () => ({foo: 1});

換行節(jié)

箭頭函數(shù)在參數(shù)和箭頭之間不能換行指黎。

var func = ()
           => 1; 
// SyntaxError: expected expression, got '=>'

解析順序節(jié)

雖然箭頭函數(shù)中的箭頭不是運(yùn)算符，但箭頭函數(shù)具有與常規(guī)函數(shù)不同的特殊運(yùn)算符優(yōu)先級解析規(guī)則州丹。

let callback;

callback = callback || function() {}; // ok

callback = callback || () => {};      
// SyntaxError: invalid arrow-function arguments

callback = callback || (() => {});    // ok

更多示例節(jié)

// 空的箭頭函數(shù)返回 undefined
let empty = () => {};

(() => 'foobar')(); 
// Returns "foobar"
// (這是一個(gè)立即執(zhí)行函數(shù)表達(dá)式,可參閱 'IIFE'術(shù)語表) 

var simple = a => a > 15 ? 15 : a; 
simple(16); // 15
simple(10); // 10

let max = (a, b) => a > b ? a : b;

// Easy array filtering, mapping, ...

var arr = [5, 6, 13, 0, 1, 18, 23];

var sum = arr.reduce((a, b) => a + b);  
// 66

var even = arr.filter(v => v % 2 == 0); 
// [6, 0, 18]

var double = arr.map(v => v * 2);       
// [10, 12, 26, 0, 2, 36, 46]

// 更簡明的promise鏈
promise.then(a => {
  // ...
}).then(b => {
  // ...
});

// 無參數(shù)箭頭函數(shù)在視覺上容易分析
setTimeout( () => {
  console.log('I happen sooner');
  setTimeout( () => {
    // deeper code
    console.log('I happen later');
  }, 1);
}, 1);

箭頭函數(shù)也可以使用條件（三元）運(yùn)算符：

var simple = a => a > 15 ? 15 : a;
simple(16); // 15
simple(10); // 10

let max = (a, b) => a > b ? a : b;

箭頭函數(shù)內(nèi)定義的變量及其作用域

// 常規(guī)寫法
var greeting = () => {let now = new Date(); return ("Good" + ((now.getHours() > 17) ? " evening." : " day."));}
greeting();          //"Good day."
console.log(now);    // ReferenceError: now is not defined 標(biāo)準(zhǔn)的let作用域

// 參數(shù)括號內(nèi)定義的變量是局部變量（默認(rèn)參數(shù)）
var greeting = (now=new Date()) => "Good" + (now.getHours() > 17 ? " evening." : " day.");
greeting();          //"Good day."
console.log(now);    // ReferenceError: now is not defined

// 對比：函數(shù)體內(nèi){}不使用var定義的變量是全局變量
var greeting = () => {now = new Date(); return ("Good" + ((now.getHours() > 17) ? " evening." : " day."));}
greeting();           //"Good day."
console.log(now);     // Fri Dec 22 2017 10:01:00 GMT+0800 (中國標(biāo)準(zhǔn)時(shí)間)

// 對比：函數(shù)體內(nèi){} 用var定義的變量是局部變量
var greeting = () => {var now = new Date(); return ("Good" + ((now.getHours() > 17) ? " evening." : " day."));}
greeting(); //"Good day."
console.log(now);    // ReferenceError: now is not defined

箭頭函數(shù)也可以使用閉包：

// 標(biāo)準(zhǔn)的閉包函數(shù)
function A(){
      var i=0;
      return function b(){
              return (++i);
      };
};

var v=A();
v();    //1
v();    //2

//箭頭函數(shù)體的閉包（ i=0 是默認(rèn)參數(shù)）
var Add = (i=0) => {return (() => (++i) )};
var v = Add();
v();           //1
v();           //2

//因?yàn)閮H有一個(gè)返回醋安，return 及括號（）也可以省略
var Add = (i=0)=> ()=> (++i);

箭頭函數(shù)遞歸

var fact = (x) => ( x==0 ?  1 : x*fact(x-1) );
fact(5);       // 120

規(guī)范

| Specification | Status | Comment |
| ECMAScript 2015 (6th Edition, ECMA-262)
<small lang="zh-CN" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px;">Arrow Function Definitions</small> | Standard | Initial definition. |
| ECMAScript Latest Draft (ECMA-262)
<small lang="zh-CN" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px;">Arrow Function Definitions</small> | Draft | |

瀏覽器兼容節(jié)

Update compatibility data on GitHub

<abbr class="only-icon" title="See implementation notes" style="font-style: normal !important; padding: 0px; border: 0px; cursor: help; text-decoration: none; margin: 0px 2px;">Notes</abbr>

打開 | <abbr class="bc-level-no only-icon" title="No support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">No support</abbr>No | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>32 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>10 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>45 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>45 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>Yes | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>22

<abbr class="only-icon" title="See implementation notes" style="font-style: normal !important; padding: 0px; border: 0px; cursor: help; text-decoration: none; margin: 0px 2px;">Notes</abbr>

打開 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>32 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>10 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>5.0 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>Yes |
| Trailing comma in parameters | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>58 | <abbr title="Compatibility unknown; please update this." style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">?</abbr> | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>52 | <abbr class="bc-level-no only-icon" title="No support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">No support</abbr>No | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>45 | <abbr title="Compatibility unknown; please update this." style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">?</abbr> | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>58 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>58 | <abbr title="Compatibility unknown; please update this." style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">?</abbr> | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>52 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>45 | <abbr title="Compatibility unknown; please update this." style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">?</abbr> | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>7.0 | <abbr class="bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: none;">Full support</abbr>Yes |

Legend

<dl style="font-style: normal !important; margin: 0px 0px 20px; padding: 0px; border: 0px; box-sizing: border-box; max-width: 42rem; display: grid; grid-template-columns: 30px 1fr 30px 1fr;">

<dt style="padding: 0px; border: 0px; font-style: normal; font-weight: 700; display: block; margin: 0px 0px 5px;"><abbr class="bc-level bc-level-yes only-icon" title="Full support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: underline dotted;">Full support </abbr></dt>

<dd style="font-style: normal !important; padding: 0px 0px 0px 20px; border: 0px; display: block; margin: 0px 10px 5px;">Full support</dd>

<dt style="padding: 0px; border: 0px; font-style: normal; font-weight: 700; display: block; margin: 0px 0px 5px;"><abbr class="bc-level bc-level-no only-icon" title="No support" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: underline dotted;">No support </abbr></dt>

<dd style="font-style: normal !important; padding: 0px 0px 0px 20px; border: 0px; display: block; margin: 0px 10px 5px;">No support</dd>

<dt style="padding: 0px; border: 0px; font-style: normal; font-weight: 700; display: block; margin: 0px 0px 5px;"><abbr class="bc-level bc-level-unknown only-icon" title="Compatibility unknown" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: underline dotted;">Compatibility unknown </abbr></dt>

<dd style="font-style: normal !important; padding: 0px 0px 0px 20px; border: 0px; display: block; margin: 0px 10px 5px;">Compatibility unknown</dd>

<dt style="padding: 0px; border: 0px; font-style: normal; font-weight: 700; display: block; margin: 0px 0px 5px;"><abbr class="only-icon" title="See implementation notes." style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px; cursor: help; text-decoration: underline dotted;">See implementation notes.</abbr></dt>

<dd style="font-style: normal !important; padding: 0px 0px 0px 20px; border: 0px; display: block; margin: 0px 10px 5px;">See implementation notes.</dd>

</dl>

相關(guān)鏈接節(jié)

• "ES6 In Depth: Arrow functions" on hacks.mozilla.org

</article>

文檔標(biāo)簽和貢獻(xiàn)者

標(biāo)簽：

• ECMAScript 2015

• ES6 Arrow Function

• Functions

• Intermediate

• JavaScript

• Lambda

• Lambda Expression

• ramda

• Reference

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最后編輯者: wangbangkun, <time datetime="2018-07-30T01:34:50.215940-07:00" style="font-style: normal !important; margin: 0px; padding: 0px; border: 0px;">Jul 30, 2018, 1:34:50 AM</time>

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1. Web 技術(shù)文檔
2. Java<wbr style="font-style: normal !important;">Script
3. Java<wbr style="font-style: normal !important;">Script 參考文檔
4. 函數(shù)
5. 箭頭函數(shù)

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箭頭函數(shù)傳參之用變量解構(gòu)的方式來傳參

let set = ({num1,num2}) => {
            return num1 + num2;
        } 
        console.log(set({num1:3,num2:4}))

普通方式傳參

 let set = (num1,num2) => {
            return num1 + num2;
        } 
        console.log(set(3,4))

    `//箭頭函數(shù)簡單版`
    // 1、當(dāng)函數(shù)參數(shù)只有一個(gè)的時(shí)候墓毒，()可以省略吓揪，但是沒有參數(shù)的時(shí)候，括號不可以省略
    //2所计、當(dāng)函數(shù)體{}中只有一行return語句的時(shí)候柠辞，中括號以及return語句可以省略。
    //以下是個(gè)例子

        let add = a => a;  
        console.log(add(3));