neko.js - Lightweight JavaScript Classes

Neko.js provides classical inheritance for JavaScript, it does so in a lightweight manner with nearly no overhead when on instantiation.

It works both in browsers (IE6+) and all versions of Node.js.

Features

• Multiple inheritance
• Static methods and properties
• Really fast creation of instances
• Ability to call unbound methods
• Passing Classes as constructors

Syntax

Class (constructor, [base1[, base2[, ... baseN]],], [methods])
Class (constructor, [base1[, base2[, ... baseN]],]).extend(methods)
Class (methods)

Creating some Classes

// A simple Animal class
var Animal = Class(function(name) { // the constructor
    this.name = name; // an instance variable

}, { // extending the class with some methods
    speak: function(words) { // a simple method
        console.log(words);
    }
});


// Let's create a class called "Cat" that inherits from Animal
var Cat = Class(function(name, color) {

    Animal.init(this, name); // call Animals constructor, basically super()
    this.color = color;

    // private variable and a getter
    var fur = 'soft';
    this.furType = function() {
        return fur;
    }

    this.$list.push(this); // push this instance into the static list of Cat

}, Animal, {  // base classes
    meow: function() {
        this.speak('Meow! My name is ' + this.name + '.'); // calling the inherited method
    },

    getColor: function() {
        return this.color;
    },

    $list: [], // let the Cat class keep track of the cats, with a static property
               // static properties are shallow copies per class

    $info: function(cat) { // static method of Cat, note the $ prefix
        return {name: cat.name, color: cat.color, fur: cat.furType()};
    },

    $listCats: function() {
        return this.$list; // this inside static methods refers to the class
    }
});

Trying them out

> kitten = new Cat('Kitty', 'black'); // create a kitten
{ name: 'Kitty', color: 'black', furType: [Function] }

> kitten.meow(); // call the instance method
Meow! My name is Kitty.

> Cat.meow(kitten); // we can also call the unbound method

> kitten.getColor(); // another call
black

> Cat.$info(kitten); // call the static method
{ name: 'Kitty', color: 'black', fur: 'soft' }

> kitten.$listCats() // get a list of the cats, by calling the static method
[ { name: 'Kitty', color: 'black', furType: [Function] } ]

More Tricks

// Creating some kind of a template
var CuteThing = Class(function() {
    this.cuteThingsDone = 0;

}, {
    cuteAction: function() {
        this.cuteThingsDone++;
        return this.doAction(); // doAction is abstract
    }
});

// Just pass the CuteThing class as the constructor
var Kitten = Class(CuteThing, {
    doAction: function() {
        return 'Doing some cute kitten thing!';
    }
});

var Puppy = Class(CuteThing, {
    doAction: function() {
        return 'Doing some cute puppy thing!';
    }
});

> new Kitten().cuteAction()
'Doing some cute kitten thing!'

> new Puppy().cuteAction()
'Doing some cute puppy thing!'