Introduction to the Apply () method and the call () method in JavaScript

1. Each function contains two non-inherited methods: Apply () and call ().
2. They are used in the same way, and are called functions in a specific scope.
3, the receiving parameters are different, apply () receives two parameters, one is the function run scope (this), and the other is a parameter array.
The first parameter of the call () method is the same as the Apply () method, but the arguments passed to the function must be enumerated.

Example 1:

Window.firstname = "Diz"= "song"var myObject = {firstName: "My", LastName: "Object"  function Helloname () {console.log (this. LastName, "Glad to meet you!" //

The result of the operation is:
Hello Diz song glad to meet you!
Hello my Object glad to meet you!

Example 2:

function sum (NUM1, num2) {  return num1 +// //

Analysis: in Example 1, we found that the real use of apply () and call () is to be able to expand the scope of the function to run, if we want to implement the traditional method, see the following code:

 window.firstname = "Diz"  =" song ";  var  myObject = {firstName: "My", LastName: "Object"  };  function   Helloname () {Console.log (  "Hello" + this . FirstName + "" + this . LastName, "Glad to meet you!" ); } helloname ();  // hello Diz song glad to meet you!  Myobject.helloname = Helloname; Myobject.helloname ();  // hello my Object glad to meet you!  

See Accents's code, we find that to make the Helloname () function scoped on the object MyObject, we need to dynamically create the Helloname property of the MyObject, which points to the Helloname () function as a pointer, so that When we call Myobject.helloname (), the This variable inside the function points to MYOBJECCT, and you can call the internal other public properties of the object.
By analyzing example 2, we can see the real use of the call () and apply () functions, and in the actual project, it is necessary to deal with the actual flexibility!
A small problem: take a look at the case of the this variable when defining a function in a function

function Temp1 () {console.log(this//function  temp2 () {Console.log (
   
    this
    
    /
    /
    var Obj =
    
    //　　　　
    
   

The execution results are the same as the following:

function Temp1 () {console.log(thisfunction  temp2 () {console.log (this  var Obj =

4. Bind () method

Browsers that support this approach are ie9+, firefox4+, safari5.1+, opera12+, and Chrome. It is a method that belongs to ECMAScript5. See examples directly:

Window.color = "Red"var o = {color: "Blue"function  saycolor () {alert (  this var osaycolor =//  

Here, Saycolor () calls the Bind () method, passes in the O object, returns the Osaycolor () function, and in Osaycolor (), the value of this is an O object.

Introduction to the Apply () method and the call () method in JavaScript