Example analysis of this keyword usage example in JavaScript

This example summarizes the usage of this keyword in JavaScript. Share it for your reference, as follows:

Example 1:

function a(){
  var user = "yao";
  ();//undefined
  (this);//window
}
a();

Equivalent to:

function a(){
  var user = "yao";
  ();//undefined
  (this);//window
}
();

This points to window.

Example 2:

var o = {
  user:"yao",
  fn:function () {
    ();//yao
  }
}
();

This points to o.

Example 3:

var o = {
  user:"yao",
  fn:function () {
    ();//yao
  }
}
();

This points to o.

var o = {
  a:10,
  b:{
    a:12,
    fn:function () {
      ();//12
    }
  }
}
();

This points to b.

Example 4:

var o = {
  a:10,
  b:{
    a:12,
    fn:function () {
      ();//undefined
      (this);//window
    }
  }
};
var j = ;
j();

In summary:

This pointer is always the object that ultimately calls it.

When this encounters the return of the function:

Example 5:

function fn(){
   = "yao";
  return {};
}
var a = new fn;
();//undefined

Example 6:

function fn(){
   = "yao";
  return function(){};
}
var a = new fn;
();//undefined

Example 7:

function fn(){
   = "yao";
  return 1;
}
var a = new fn;
();//yao

Example 8:

function fn(){
   = "yao";
  return undefined;
}
var a = new fn;
();//yao

This points to the object returned by the function.

function fn(){
   = "yao";
  return null;
}
var a = new fn;
();//yao

Although: null is an object, this is still pointing to an instance of the function at this time.

PS：

In "use strict" mode, this default pointing is undefined, not window.

For more information about JavaScript, readers who are interested in reading this site's special topic:JavaScript object-oriented tutorial》、《Summary of common JavaScript functions techniques》、《Summary of JavaScript Errors and Debugging Skills》、《Summary of JavaScript data structure and algorithm techniques》、《JavaScript traversal algorithm and skills summary"and"Summary of JavaScript mathematical operations usage》

I hope this article will be helpful to everyone's JavaScript programming.