The this point problem in JS

there is no relationship between this point in the function and where the current function is defined or executed.
The following rules are analyzed for this point:

[non-strict mode]
1. This is always the window in the self-executing function
[Case 1]
var obj={
fn: (function (i) {
//this->window
return function () {
//this->obj
       }
}) (0)
 };
Obj.fn ();

2. Bind a method to an element's behavior, and when the behavior is triggered, the method of binding is executed, and this is the current element in the method .
[Case 1]
odiv.onclick=function () {
//this->odiv
 };

[Case 2]
function fn () {
//this->window
 }
odiv.onclick=function () {
//this->odiv
fn ();
 };

3, method execution, look at the method name before the ".", if there is, "." Who's in front, this is who, no, this is window.
[Case 1]
var obj={fn:fn};
function fn () {}
fn.prototype.aa=function () {};
var f=new fn;

fn ();//this->window
Obj.fn ();//this->obj
Fn.prototype.aa ();//this->fn.prototype
F.aa ();//this->f
F.__proto__.aa ();//this->f.__proto__->fn.prototype


4, in the constructor mode, the this.xxx=xxx in the function body is an instance of the current class
[Case 1]
function Fn () {
this.x=100;//this->f
this.getx=function () {
Console.log (this);//this->f because the Getx method executes, "." The front is F, so this is the F
    }
 }
var f=new Fn;
f.getx ();

5, the use of call/apply to change the direction of this (but encountered call/apply the above four are useless)


[Strict mode]
the "use strict";//-> tells the browser that the JS code we're writing next uses strict mode

1. This in self-executing function is always undefined
[Case 1]
var obj={
fn: (function (i) {
//this->undefined
return function () {
//this->obj
       }
}) (0)
 };
Obj.fn ();

3, method execution, look at the method name before the ".", if there is, "." Who's in front of this is who, if not, this is undefined.
[Case 1]
var obj={fn:fn};
function fn () {}

fn ();//this->undefined
Obj.fn ();//this->obj

we find that this is the main difference between this and the non-strict mode in strict mode: In the case that there is no write execution body in the JS code, the default is window execution in the non-strict mode, so this point is the window, but in strict mode, No writing is no Executive body, this point is undefined;

The this point problem in JS