Detailed explanation of the simple usage of apply and call in js

Call and apply appear to dynamically change this. When an object does not have a certain method, but others do, we can use call or apply to operate with the methods of other objects. This article mainly introduces the simple usage of apply and call in js in detail. It has certain reference value. Interested friends can refer to it. I hope it can help everyone.

call and apply are methods of Function.prototype, which are implemented internally by the JavaScript engine. Because they belong to Function.prototype, each Function object instance, that is, each method has call and apply attributes. .Since they are attributes of methods, their use is of course specific to methods. These two methods are easily confused because they have the same function, but they are just used in different ways.
From the above, we can conclude that call, apply It is used for methods, in order to change the this pointer of calling the method

Simple example:

call

function A() {
  this.getName = function (xx) {
    return xx;
  }
}

function B() {

}

var a = new A();
console.log( a.getName('i am A') ); //i am A

var b = new B() ;
console.log( a.getName.call(b,'i am B') ); // i am B

B function does not have any method, A function has getName( ) method, a.getName() is naturally established, but what if B also needs to use the getName() method? Then use call(this,'parameter')! !

You can understand this sentence again - we can use call or apply to call other objects' methods to operate. Call and apply appear to dynamically change this. Originally a.getName()'s this points to a, call dynamically points this to b and becomes b.getName()

apply

apply and call only use different parameters

function A() {
  this.sun = function (a ,b) {
    return a+b;
  }
}

function B() {

}

var a = new A();
console.log( a.sun(1,2) ); //3

var b = new B() ;
console.log( a.sun.call(b,2,2) ); // 4

console.log( a.sun.apply(b,[3, 3]) ); //6

General usage of call and apply

are commonly used. The dom node selected through document.getElementsByTagName is an array-like array. It cannot apply push, pop and other methods under Array. We can pass:

var domNodes = Array.prototype.slice.call(document.getElementsByTagName("*"));

so that domNodes can apply all methods under Array.

Related recommendations:

javascript changes the apply and call usage examples pointed to inside the function body Detailed explanation

call in js () and apply() understanding

This in Js points to the problem of apply().call(),bind()

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