javascript 箭头函数

箭头函数返回对象加()

//箭头函数返回对象的时候要加个()
      var fnc = () => ({
          name: 'zong',
          age: 33
      })

箭头函数没有this, arguments

**箭头函数没有this**

doSomethingLater: function() {
          console.log(this)
          //since the arrow function was created within the "obj"
          //即箭头函数在哪里定义的，this就指向哪个作用域
        //   setTimeout(() => {
        //       this.count++
        //       console.log(this.count)
        //   }, 2000)

        //但凡创建一个函数就会创建新的相应的作用域链,这里的回调函数是系统调用的，指向window
        setTimeout(function() {
              console.log(this)
              this.count++
              console.log(this.count)
          }, 2000)
      }

 **没有绑定 arguments**

var argument = [1, 2, 3]
  var arr = () => argument[0]
  console.log(arr())

  function foo(n) {
      //console.log(arguments)
      //这里arguments[0] 就是 n
      //var f = (arg) => arg + n
      var f = () => {
          //箭头函数的arguments也是外层函数foo的
        //console.log(arguments)
        console.log(arguments[0],arguments[1],n)
        return arguments[1] + n
      }
      //var f = () => argument[0] + n
      return f(11)
    //   var f = (...args) => args[0] + n
    //   return f(6)
  }
  console.log(foo(3,8))

箭头函数不能用来new 对象

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

箭头函数不能使用原型链

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

call/apply/bind不能用在箭头函数上

var obj = {
    num: 100
}

// Setting "num" on window to show how it gets picked up.
window.num = 2020; // yikes!

// Arrow Function
var add = (a, b, c) => this.num + a + b + c;

// call
console.log(add.call(obj, 1, 2, 3)) // result 2026

// apply
const arr = [1, 2, 3]
console.log(add.apply(obj, arr)) // result 2026

// bind
const bound = add.bind(obj)
console.log(bound(1, 2, 3)) // result 2026

箭头函数解析顺序,要用()包装成对象使用

let callback;

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

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

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

本文由 dealdot ＜dealdot＃163.com＞ 创作, Full Stack Developer @ DeepBlue
本文最后编辑时间为: Apr 17, 2021 at 17:34 pm
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