Detailed explanation of javascript closure var that=this

Quick Overview

var f1  = function(){
    var a = 999;
    nAdd = function(){n+=1}    //没有var，nAdd是全局变量
    f2 = function(){
        alert(a)
    }
    return f2;
}
var result = f1();
result();    //999
nAdd();        //相当于一个setter，可以在函数外部操作函数内部变量的值
result();    //1000,f2()被执行了2次

The concept of closure

Function within a function

The purpose of closure

You can read variables inside the function
Always keep the variables of the parent function in memory
Note: If you want to keep the variable values ​​of the parent function unchanged, you need to use the parent function as an object

---

//父函数作对象
var name = 'The Window';
var object = {
    name : 'The Object',
    getName : function(){
        return function(){
            return this.name
        }
    }
}

alert(object.getName()())    //The Window

var that = this;

var _name = 'The Window';
var object = {
    _name : 'The Object',    //_name 下划线表示私有变量
    getName : function(){
        var that = this;
        return function(){
            return that._name;
        }
    }
}

alert(object.getName()())    //The Object

that=this / _this=this

##Learn Javascript Closure (Closure) (Ruan Yifeng)

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Detailed introduction to JavaScript closures

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