看完javascript高级教程对this对象的理解_怎么理解内部函数永远不能直接访问外部函数的this和argunebts

对于this的指向我自己总结下来，大概分四个环境

1.在全局中调用

this = window   // 这个就不做过多说明
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2.在标准函数中调用,this指向调用该函数的上下文。

window.color = 'red'
let o = { color: blue}
function saycolor() {
  consloe.log(this.color)
}
saycolor() // red	this = window  
o.saycolor = saycolor
o.saycolor()  // blue	this = o
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3.在箭头函数中调用,this指向定义该箭头函数的上下文。

window.color = 'red'
let o = { color: blue}
let saycolor = () => {
  consloe.log(this.color)
}
saycolor() // red	this = window  
o.saycolor = saycolor
o.saycolor()  // red	this = window
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4.在定时器中，this不做特殊指向则指定window

var name = 'my name is window';
  var obj ={
     name:'my name is obj',
      fn:function(){
          var timer = null;
          clearInterval(timer);
          timer = setInterval(function(){
          console.log(this.name)//my name is window
      },1000)
    }
}
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5.在闭包中，内部函数不能直接访问到外部函数的this与argument，若果想访问到则可以把this保存到闭包可以访问到的变量上去。

window.identity = 'the window'
let object = {
  identity = 'the object'
  getdentityFunc() {
	return function() {
	  return this.identity
	}
  }
}
console.log(object.getdentityFunc()())  //the window

// 把this保存到闭包可以访问到的变量上去。

window.identity = 'the window'
let object = {
  identity = 'the object'
  getdentityFunc() {
    let that = this
	return function() {
	  return that.identity
	}
  }
}
console.log(object.getdentityFunc()())  //the object

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