Why do we have Function.call in javascript? - Stack Overflow

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> Function.call == Function.prototype.call
true
> Function.prototype == Function
false

Why do Function.prototype.* methods exist as Function.*? It seems inconsistent.

This isn't the case with any other primary type (Array.slice doesn't exist but Array.prototype.slice does).

> Function.call == Function.prototype.call
true
> Function.prototype == Function
false

Why do Function.prototype.* methods exist as Function.*? It seems inconsistent.

This isn't the case with any other primary type (Array.slice doesn't exist but Array.prototype.slice does).

• javascript

Share Improve this question Follow edited Jan 15, 2016 at 9:33 thefourtheye 240k5353 gold badges465465 silver badges500500 bronze badges asked Jan 15, 2016 at 9:06 Louay AlakkadLouay Alakkad 7,40822 gold badges2424 silver badges4545 bronze badges

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1 Answer 1

Sorted by: Reset to default 18

Because Function itself is the prototype of Function

console.log(Function instanceof Function);
console.log(Object.getPrototypeOf(Function) === Function.prototype);

So, all the functions in the Functions prototype are available in Function also.

Quoting the specification,

The Function prototype object is itself a Function object (its [[Class]] is "Function")

---

Another way to confirm this would be,

console.log(Function.call === Function.prototype.call);

it means that the Function.call object and Function.prototype.call object are the same.

console.log(Function.hasOwnProperty('call'));

it means that the Function object itself doesn't have call property.

console.log(Function.prototype.hasOwnProperty('call'));

it means that Function.prototype object has the call property.

---

Array.slice doesn't exist but Array.prototype.slice do

Because Array function's prototype is Function object, not the Array object.

console.log(Object.getPrototypeOf(Array) === Function.prototype);

That is why we get call, apply, bind etc on the Array function. It Array object had been the prototype of Array, then slice would have been available on the Array object also.

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