Definition of apply and call methods and the difference between apply and call methods_javascript skills

If you have never been exposed to dynamic languages, it will feel magical and weird to understand JavaScript with the way of thinking of compiled languages, because things that are consciously impossible often happen, and even feel unreasonable. If you are learning When you encounter this feeling in the process of JavaScript, a free and ever-changing language, then from now on, please put down your "prejudice", because this is definitely a new continent for you. Okay, let’s not talk to you anymore. Let’s get back to the business. Let me first explain to you the definitions of the apply and call methods.

The specific content is as follows:

1. Method definition

call and apply both belong to a method of Function.prototype, which is implemented internally by the JavaScript engine. Because it belongs to Function.prototype, each Function object instance, that is, each method has call and apply attributes. Since as Attributes of methods, then their use is of course specific to methods. These two methods are easy to confuse because they have the same function, but they are used in different ways.

call method:

Syntax: call([thisObj[,arg1[, arg2[, [,.argN]]]]])

Definition: Call a method of an object to replace the current object with another object.

Description:

The call method can be used to call a method on behalf of another object. The call method changes the object context of a function from the initial context to the new object specified by thisObj.

If no thisObj parameter is provided, the Global object is used as thisObj.

apply method:

Syntax: apply([thisObj[,argArray]])

Definition: Apply a method of an object to replace the current object with another object.

Description:

If argArray is not a valid array or is not an arguments object, a TypeError will be caused.

If neither argArray nor thisObj is provided, the Global object will be used as thisObj and no parameters can be passed

The function of call and apply is to borrow other people’s methods to call, just like calling your own.

Their differences:

apply: There can only be two parameters at most - the new this object and an array argArray. If multiple parameters are passed to this method, all parameters will be written into this array. Of course, even if there is only one parameter, it will be written into the array. If argArray is not a valid array or is not an arguments object, a TypeError will be caused. If neither argArray nor thisObj are provided, the Global object will be used as thisObj and no parameters can be passed.

call: It is a direct parameter list, mainly used when various methods of js objects call each other to keep the current this instance pointer consistent, or to change this pointer under special circumstances. If the thisObj parameter is not provided, the Global object is used as thisObj.

To put it more simply, the functions of apply and call are the same, but the form of the parameter list passed in is different: for example, the corresponding apply writing method of func.call(func1,var1,var2,var3) is:

func.apply(func1,[var1,var2,var3])

For example:

add.apply(sub,[3,1]);
//add.call(sub,3,1);
var a={
n:1,
m:2,
add:function(){
return this.n+this.m;
}
}
var b={n:3,m:4
}
console.log(a.add.call(b));//b.n+b.m=7
function Animal(){ 
this.name = "Animal"; 
this.showName = function(){ 
alert(this.name); 
} 
}
function Cat(){ 
this.name = "Cat"; 
} 
var animal = new Animal(); 
var cat = new Cat(); 
//通过call或apply方法，将原本属于Animal对象的showName()方法交给对象cat来使用了。 
//输入结果为"Cat" 
animal.showName.call(cat,","); 
animal.showName.apply(cat,[]);

The above content is the definition of apply and call methods and the difference between apply and call methods introduced by the editor. I hope you like it.