func.prototype.constructor是否与func完全相同？

Question

function A(name){
    this.name=name;
}

If A===A.prototype.constructor then invoking both of them does not set the name variable on window object

Only A("abhishek") sets the variable on window and A.prototype.constructor("randommm") does not!

Can someone please explain what's the difference, I am thinking that

A.prototype.constructor("randommm")

is called from a different context?

Answer 1

Yes, they run in different contexts.

You're creating a hoisted function in the local scope, which means its default context, unless you bind it to something else, will be window (or at any rate the global namespace) when you invoke it.

Calling it via prototype.constructor , though, calls it as a method of the prototype object, so it's logical that the prototype is the context.

function A() { alert(this); }
A(); //context = window
A.prototype.constructor(); //context = prototype

Fiddle .

Answer 2

Yes:

A()

calls the function with this being window

A.prototype.constructor("randommm")

calls the constructor property of A.prototype which is its context.

However i don't see the sense of calling a constructor without new ...

Answer 3

A.prototype.constructor("randommm") is setting the property name on A.prototype :

 function A(name){ this.name=name; } A.prototype.constructor("John Doe"); console.log(A.prototype.name); // John Doe 

The value of this will be whatever before the . in the call to the function (unless, ofcourse, it is explicitly specified using bind ).

Answer 4

as a side note if you really want to use the constructor instead of function this

A.prototype.constructor.bind(this)("randommm")

works. But I think it doesn't make any sense in this case

Answer 5

The function being called is the same in both cases, what changes is the context in which it is being called.

Here the function is called on its own, so it uses global context:

A("abhishek") 

Here the function is called on A.prototype, so it uses A.prototype context:

A.prototype.constructor("randommm")