This article will help you quickly understand the use of call functions in JavaScript

Before understanding the call() function, you must first understand the pointing problem of this

This points to

1. Point to window:

var name = 'Little Red' 
function foo () { 
    () //Xiaohong} 
foo() //The direct call method points to window

2. Point to the direct caller:

var name = 'Little Red'
var object = {
    name: 'Li Bai',
	function foo () {
	  () //Li Bai	}
}
() //Object calls foo() directly, this points to object

3. Point to new instance:

var name = 'Little Red' 
function foo () { 
     = 'noob' 
    () //noob} 
var fn = new foo() //This points to the instance fn of foo()

This is a problem that is easier to understand

To sum up, it's just one sentence:Whoever calls the function, this is who

Let’s talk about the call() function. Call() is different from our normal thinking mode. If the brain circuit turns around,

Call() points to

In a simple sentence: (A) <==>A calls function B, which can be interpreted as B's this pointing to A.

Code example:

function _add() {  
    ();  
}  
function _sub() {  
     = 222;
    ();  
}  
_add.call(_sub); //Output undefined.  At this time, this of _add points to _sub,_subInsidethisPoint to Yeswindow，so_subNo itselftestThis property

_add.call(new _sub())//Output 222.  At this time, this of _add points to _sub,_subInsidethisPoint to Yes_subExample，Can be obtained_suboftestproperty，so输出222

/******************************************************/
function _add() {  
     = 444
    ();  
}  
function _sub() {  
     = 222;
    ();  
}  
_add.call(_sub); //Output 444.  At this time, this pointing to window in _sub,

Therefore, there is no test attribute in _sub, but this of _add points to _sub and creates a test attribute for _sub, so the value of test is 444

If you think what you said above is not easy to understand, there are ways to easily remember

Cats eat fish, dogs eat meat, Ultraman fights small monsters.
One Tenggou wants to eat fish
Cat.Eating fish.call (dog, fish) // The function called by the dog to eat fish, so this is a dog
The dog eats the fish
The cat has become a spirit and wants to fight monsters
Ultraman. Killing the little monster.call (cat, little monster) // The cat calls the function to kill the monster, so this is a cat

More simple,

Jack Ma will make money
I used the call() function to borrow Jack Ma's money-making function.
So I'll make money, too
Jack Ma. Make Money.call(me)
This pointes to me at this moment
Because it is the money-making function I called

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