Developers coming from Java to JavaScript are often surprised at JavaScript's lack of class support. An object-oriented—as well as functional—language, JavaScript supports object-oriented constructs via a prototype system.

Because prototypes are a somewhat foreign notion to those used to working with classes, many JavaScript libraries and frameworks aim to provide some notion of classes, including inheritance based on classes. In a recent blog post, Simple JavaScript Inheritance, John Resig, author of the JQuery library, explains how to provide a simple class-like facility to specify inheritance for JavaScript.

Using Resig's techniques allows developers to write code in a more familiar style, such as:

var Person = Class.extend({
  init: function(isDancing){
    this.dancing = isDancing;
  },
  dance: function(){
    return this.dancing;
  }
});
var Ninja = Person.extend({
  init: function(){
    this._super( false );
  },
  dance: function(){
    // Call the inherited version of dance()
    return this._super();
  },
  swingSword: function(){
    return true;
  }
});

Resig highlights the most important benefits of his technique:

• Creating a constructor had to be simple (in this case simply providing an init method does the trick).
• In order to create a new 'class' you must extend (sub-class) an existing class.
• All of the 'classes' inherit from a single ancestor: Class. Therefore if you want to create a brand new class it must be a sub-class of Class.
• And the most challenging one: Access to overridden methods had to be provided (with their context properly set). You can see this with the use of this._super(), above, calling the original init() and dance() methods of the Person super-class.

The rest of Resig's blog post describes the technique in detail, and shows why it yields an easier programming model than a more straightforward use of prototypes.

What do you think of Resig's technique? Which JavaScript library do you find the easiest to use for OO development?