The difference between call() and apply() in JavaScript_javascript tips

If you have never been exposed to dynamic languages, it will be a magical and weird feeling 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, let JavaScript

Okay, let’s get back to the subject. First, understand the dynamic change runtime context feature of JavaScrtipt. This feature is mainly reflected in the use of the apply and call methods.

1. Definition of method

call method:

Syntax: call(thisObj, Object)

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.

-------------------------------------------------- ----------------------------------

Note: The call and apply methods are exactly the same, except that apply uses an array to pass parameters.

Code example:

function Animal(name) {
this.name = name;
this.showName = function() {
console.log(this.name);
};
}
function Cat(name) {
Animal.call(this, name);
}
Cat.prototype = new Animal();
function Dog(name) {
Animal.apply(this, name);
}
Dog.prototype = new Animal();
var cat = new Cat("Black Cat"); //call必须是object
var dog = new Dog(["Black Dog"]); //apply必须是array
cat.showName();
dog.showName();
console.log(cat instanceof Animal);
console.log(dog instanceof Animal); 

-------------------------------------------------- --------------------------------

Simulate call, apply this replacement

function Animal(name) {
this.name = name;
this.showName = function() {
alert(this.name);
};
};
function Cat(name) {
this.superClass = Animal;
this.superClass(name);
delete superClass;
}
var cat = new Cat("Black Cat");
cat.showName();

Summary:

Their respective definitions:

apply: Apply a method of an object and replace the current object with another object.

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

What they have in common:

Both "can be used to call a method instead of another object, changing the object context of a function from the initial context to the new object specified by thisObj." - Excerpted from JScript5.5.chm

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 no thisObj parameter is 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])