Object-Oriented JavaScript - Second Edition

Inheriting the prototype only

As explained previously, for reasons of efficiency you should add the reusable properties and methods to the prototype. If you do so, then it's a good idea to inherit only the prototype, because all the reusable code is there. This means that inheriting the Shape.prototype object is better than inheriting the object created with new Shape(). After all, new Shape() only gives you own shape properties that are not meant to be reused (otherwise they would be in the prototype). You gain a little more efficiency by:

• Not creating a new object for the sake of inheritance alone
• Having less lookups during runtime (when it comes to searching for toString() for example)

Here's the updated code; the changes are highlighted:

function ...