The magic call () method in JavaScript, javascriptcall

The magic call () method in JavaScript, javascriptcall

First, let's take a look at the official explanation of call (). "call a method of an object and replace the current object with another object .", After reading this explanation, you may be confused. Example:
Copy codeThe Code is as follows:
Var x = "I Am a global variable"; // defines the global variable x
Function a () {// define function class structure
This. x = "I declare it in function class structure ";
}
// Define a common function. The value of variable x contained in the current pointer is displayed.
Function f (){
Alert (this. x );
}
// The returned value is "I declare it in function class structure"
F. call (new ());

In my understanding, f. call (new a () is to copy function (actually an object) f to the called object "new a ()" for parsing. In fact, it is the same as the parsing result of the following code:
Copy codeThe Code is as follows:
Function (){
This. x = "I declare it in function class structure ";
Alert (this. x );
}
A ();

In this case, variable X has different scopes... It looks a little inherited, isn't it? In the preceding example, f is fully inherited by the strength object of constructor a. If this is not enough, it means. call (B) is an inheritance mode, so let's look at a more inherited usage.
Copy codeThe Code is as follows:
Function f (){
This. a = "";
This. B = function (){
Alert ("B ");
}
}
Function e (){
F. call (this );
}
Var c = new e ();
Alert (c. a); // pop up
C. B (); // pop up B

In this example, as long as a friend of the browser can see that e fully inherits the attributes and methods of f, otherwise it cannot be explained, because attributes a and B are not defined in e, it is inferred from common sense that these two attributes will not appear in Instance Object c of e.