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Dean Edward's Base javascript inheritance library ported to node.js

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Octocat-spinner-32 README.md
Octocat-spinner-32 base.js
README.md

This is a basic port of Dean Edward's Base javascript library for inheritance. You can find his original description here.

This port will be turned into a proper node.js module/package as soon as I get around to it, but for now to can be imported into a node project using the standard var Base = requires('PATH/TO/base.js');.

I'm also working on a fork of this library that adds some generic-style type checking.

Below is a copy of the blog post/documentation that Dean Edwards published for the original library:


A Base Class for JavaScript Inheritance

I'm an OO programmer at heart and JavaScript supports prototype based inheritance. Unfortunatley this leads to verbose class definitions:

function Animal(name) {};
Animal.prototype.eat = function() {};
Animal.prototype.say = function(message) {};

I want a nice base class for JavaScript OO:

  • I want to easily create classes without the MyClass.prototype cruft
  • I want method overriding with intuitive access to the overridden method (like Java's super)
  • I want to avoid calling a class' constructor function during the prototyping phase
  • I want to easily add static (class) properties and methods
  • I want to achieve the above without resorting to global functions to build prototype chains
  • I want to achieve the above without affecting Object.prototype

The Base Class

I've created a JavaScript class (Base.js) that I hope eases the pain of JavaScript OO. It's a simple class and extends the Object object by adding two instance methods and one class method.

The Base class defines two instance methods:

extend

Call this method to extend an object with another interface:

var object = new Base;
object.extend({
    value: "some data",
    method: function() {
        alert("Hello World!");
    }
});
object.method();
// ==> Hello World!
base

If a method has been overridden then the base method provides access to the overridden method:

var object = new Base;
object.method = function() {
    alert("Hello World!");
};
object.extend({
    method: function() {
        // call the "super" method
        this.base();
        // add some code
        alert("Hello again!");
    }
});
object.method();
// ==> Hello World!
// ==> Hello again!

You can also call the base method from within a constructor function.

Creating Classes

Classes are created by calling the extend method on the Base class:

var Animal = Base.extend({
    constructor: function(name) {
        this.name = name;
    },

    name: "",

    eat: function() {
        this.say("Yum!");
    },

    say: function(message) {
        alert(this.name + ": " + message);
    }
});

All classes created in this manner will inherit the extend method so we can easily subclass the Animal class:

var Cat = Animal.extend({
    eat: function(food) {
        if (food instanceof Mouse) this.base();
        else this.say("Yuk! I only eat mice.");
    }
});

var Mouse = Animal.extend();

Class Properties and Methods

A second parameter passed to the extend method of a class defines the class interface:

var Circle = Shape.extend({ // instance interface
    constructor: function(x, y, radius) {
        this.base(x, y);
        this.radius = radius;
    },

    radius: 0,

    getCircumference: function() {
        return 2 * Circle.PI * this.radius;
    }
}, { // class interface
    PI: 3.14
});

Note the use of the base method in the constructor. This ensures that the Shape constructor is also called. Some other things to note:

  • If you define a class method (not an instance method) called init it will be automatically called when the class is created
  • Constructor functions are never called during the prototyping phase (subclassing)

Classes With Private Data

Some developers prefer to create classes where methods access private data:

function Circle(radius) {
    this.getCircumference = function() {
        return 2 * Math.PI * radius;
    };
};

You can achieve the same result using the Base class:

var Circle = Shape.extend({
    constructor: function(radius) {
        this.extend({
            getCircumference: function() {
                return 2 * Math.PI * radius;
            }
        });
    }
});

The code is slightly more verbose in this case but you get access to the base method which I find incredibly useful.

Single Instances

I changed my mind a lot about this but finally decided to allow the creation of single instance classes by defining a null constructor:

var Math = Base.extend({
    constructor: null,
    PI: 3.14,
    sqr: function(number) {
        return number * number;
    }
});

Conclusion

This supersedes my old OO framework which was not as cross-browser as I would have liked (and had other shortcomings).

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