someFunction.Prototype.constructor vs someFunction.constructor

Question

I am aware of the fact that functions in JavaScript lead a dual life first of a function (as first class thing to create instances from) and the second one of a normal object.

But I am surprised to see the output of the following console.

function A() {
    console.info("A");
}
console.info(A.prototype.constructor === A.constructor); // false

I expected it to be true as I was not expecting constructor property on the object A as it's own property. And hence following the prototypical chain lookup it should have been the same object as A.prototype.constructor. Where am I wrong or what piece am I missing?

The first prototype used in A is Function.prototype because A is constructed from Function. Instances of A (aInstance = new A) will use A.prototype as the first prototype in its prototype chain because aInstance has A as it's constructor. More on prototype can be found here: stackoverflow.com/a/16063711/1641941 — HMR
– HMR, Commented Apr 24, 2015 at 11:59

Community · Accepted Answer · 2017-05-23 11:54:22Z

5

Where am I wrong or what piece am I missing?

That A does not inherit from A.prototype. A is a (constructor) function, and inherits from Function.prototype. Do a console.log(Object.getPrototypeOf(A)) :-)

From A.prototype only new A instances do inherit (whose .constructor is A). See also __proto__ VS. prototype in JavaScript.

edited May 23, 2017 at 11:54

CommunityBot

11 silver badge

answered Apr 24, 2015 at 12:22

Bergi

671k162 gold badges1k silver badges1.5k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

sachin.ph · Accepted Answer · 2015-04-24 12:14:32Z

1

That is beacuse both are returning different values.

Object.prototype.constructor

Returns a reference to the Object function that created the instance's prototype. Note that the value of this property is a reference to the function itself, not a string containing the function's name.
Function constructor

The Function constructor creates a new Function object. In JavaScript every function is actually a Function object.

Also if you console above code you will see

console.info(A.prototype.constructor); outputs

function A() {
    console.info("A");
}

console.info(A.constructor); outputs

function Function() { [native code] } // both are different.

answered Apr 24, 2015 at 12:14

sachin.ph

1,07812 silver badges24 bronze badges

Collectives™ on Stack Overflow

someFunction.Prototype.constructor vs someFunction.constructor

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related