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javascriptprototypeprototypal-inheritance
Lee
Lee

Reputation: 3969

Why declare prototype functions outside the inheriting object?

There are many questions regarding Javascript's implementation of inheritance, although I've not found an answer for why prototypes, in all examples and answers I've seen, are declared outside of the "class". Furthermore it seems using this.prototype can't be used, which seems unintuitive to those from an OOP background.

Is there any difference between:

function AClass() {
   AClass.prototype.AMethod = function(parms) { };
}

and

function AClass() { }
AClass.prototype.AMethod = function(parms) { };

Upvotes: 0

Views: 55

Answers (2)

Karolis Ramanauskas
Karolis Ramanauskas

Reputation: 1065

Every time you call AClass you are redefining AMethod if it's put inside the function scope. It slows down the code. Prototypes are useful when you will be creating many objects with duplicated functionality. Here is a similar question delving in related discussion in more detail Use of 'prototype' vs. 'this' in JavaScript?.

Upvotes: 1

Quentin
Quentin

Reputation: 943480

The difference is exactly the same as any other statement that you might put inside a function or outside a function. If it is inside the function, it runs when the function is called.

It doesn't make sense to redefine part of the "class" every single time an object is instantiated from it.

Upvotes: 3

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