Book Image

Object-Oriented JavaScript

By : Stoyan Stefanov, Stoyan STEFANOV
Book Image

Object-Oriented JavaScript

By: Stoyan Stefanov, Stoyan STEFANOV

Overview of this book

Table of Contents (18 chapters)
Object-Oriented JavaScript
About the Author
About the Reviewers
Built-in Functions
Regular Expressions

Parasitic Inheritance

I f you like the fact that you can have all kinds of different ways to implement inheritance in JavaScript, and you're hungry for more, here's another one. This pattern, courtesy of Douglas Crockford, is called parasitic inheritance. It basically means that you can have a function that creates objects by taking all of the functionality of another object, augmenting it and returning it, "pretending that it has done all the work".

Here's an ordinary object, defined with an object literal, and unaware of the fact that it is soon going to fall victim to parasitism:

var twoD = {
  name: '2D shape',
  dimensions: 2

A function that creates triangle objects could:

  • Clone the twoD object into an object called that. This can be done in any way you saw above, for example using the object() function or copying all the properties.

  • Augment that with more properties.

  • Return that.

function triangle(s, h) {
  var that = object(twoD); ='Triangle';
  that.getArea = function(...