Analysis of common situations of JavaScript this keyword pointing

  • 2021-08-10 06:36:25
  • OfStack

In the previous experience of writing code, I often try to write this, and I don't know where to point. Today, I looked at the javascript design pattern I explored, which specifically talked about the objects that this refers to in different situations, which is very interesting.

The situation referred to by this

this has the following four situations:

1. Object. Formal call of function: object. function ();

2. Formal call of ordinary function: function ();

3. Constructor call;

4. Function. prototype. call or Function. prototype. apply call;

1. Object. Formal call of function

Object. When called as a function, refers to this object.

var obj = {
    alert(this.num);// Output 1

2. Call in the form of ordinary function

When a normal function is called, this points to a global object.

window.num = 2;
var obj = {
obj.getNum();// Eject 1
var fun1 = obj.getNum;
fun1();  // Eject 2

Amazing, call the function fun () directly; Calling functions xxx. fun () through objects; this refers to different objects.

3. Constructor call

In order to use the new keyword, the creation object of javascript can be defined as follows.

var person = function(){
this. name = 'Liu Bei';

In this case, this refers to the object being created.

var p = new person();
alert (p. name); //Eject Liu Bei

4. Function. prototype. call or Function. prototype. apply call

var obj1 = {
  name:' Guan Yu ',
var obj2 = {
  name:' Liu Bei '
alert(obj1.getName());  // Guan Yu 
alert(;  // Liu Bei 

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