Detailed explanation of the usage of call(), apply() and bind() in js

I finally understand the usage of call(), apply(), and bind() in javascript

It’s actually a very simple thing. After ten minutes of careful reading, I went from being confused to fully understanding. !

First understand the following:

Example 1

##obj.objAge; //17

obj.myFun () //Xiao Zhang’s age is undefined

Example 2

shows() //Blind monk

Compare the difference between the two this, This in the first print points to obj, and in the second globally declared shows() function, this is window;

1, call(), apply(), and bind() are all used to redefine this This object!

For example:

obj.myFun.call(db); //Dema’s age is 99

obj.myFun.apply( db); //Dema’s age is 99

obj.myFun.bind(db)(); //Dema’s age is 99

Above, there is an extra () after the bind method , the results returned are consistent!

It can be concluded from this that bind returns a new function, which you must call before it will be executed

2. Compare call, bind and apply parameter passing situations

　

　

obj.myFun.call(db,'Chengdu','Shanghai');　　 //Dema is 99 years old from Chengdu to Shanghai

obj.myFun.apply(db ,['Chengdu','Shanghai']); //Dema's age is 99. From Chengdu to Shanghai

obj.myFun.bind(db,'Chengdu','Shanghai')(); // Dema's age is 99. From Chengdu to Shanghai

obj.myFun.bind(db,['Chengdu','Shanghai'])(); //Dema's age is 99. From Chengdu, to Shanghai to undefined

Subtle difference!

It is not difficult to see from the above four results
The first parameters of the three functions call, bind, and apply are all the objects pointed to by this. The difference comes from the second parameter:
The parameters of call It is put in directly. The second, third and nth parameters are all separated by commas and placed directly at the end. obj.myFun.call(db,'Chengdu', ...,'string');
　All parameters of apply are It must be placed in an array and passed in obj.myFun.apply(db,['Chengdu', ..., 'string' ]);
Except that it returns a function, bind has the same parameters as call.
　　　　
　　Of course, the parameters of the three are not limited to string type, and are allowed to be of various types, including functions, objects, etc.!

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Detailed introduction to the usage of bind, call, and apply functions in JavaScript

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