"this" in javascript

In Javascript, the key work "this" is a hard point to understand, in this artical, I will try to explain it

talking about "this", we have to talk about closure and the way function is called in Javascript.

function have for kinds of calling:

1. called as a method:

1 var s = { 2 a : '123', 3 foo:function(){ 4 return this.a 5 } 6 } 7 8 s.foo() //123

in this code, the function is called as object's method, in the closure of the function ,this point to its parent object.

2. called as a function

var a = 123; var foo = function() { var a = 456; return this.a } foo() // 123

In this code, the function is called as a function, in the code's closure, this will point to the gloable window.

3. called as a constructor

1 var Foo = function(){ 2 this.a = 1; 3 this.b = 2; 4 return this; 5 } 6 7 var foo = new Foo(); 8 foo.a //1;

 in this code, the function is called as a constructor, this will point to the new object.

4. called by .apply and .call

1 var foo = function(arg1){ 2 this.a = arg1; 3 } 4 var s = {}; 5 foo.apply(s,[1]);

 in this code, when the apply is called, this will be binded to the first param of the apply.

转载于:https://www.cnblogs.com/zhongmi/p/3850291.html