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Classic: obvious inheritance for JavaScript

Classic gives you three types of inheritance:

  • Classical inheritance through prototype chaining
  • Multiple inheritance through object composition
  • Prototypal inheritance through a cross-browser polyfill for Object.create

And, it's just about 1/2 of a Kb, minified and gzipped.
Yup, you read that right: one half of a Kb.

Example

Check it out -- define a class (constructor function):

var Bunny = classic({
  hop: function (length) { ... }
});

...and inherit from it:

var JackRabbit = classic(Bunny, {
  constructor: function (type) {
    this.type = type;
  },
  skip: function (length) { ... }
});

All prototype properties of Bunny are available to JackRabbit:

var myJackRabbit = new Jackrabbit('grey');
myJackRabbit.hop();
myJackRabbit.skip();

Multiple inheritance is also supported. Pass in any number of objects to be mixed in with the prototype:

var artist = { ... };
var musician = { ... };
var writer = { ... };
var Composer = classic(artist, musician, writer);

var myComposer = new Composer();

Mix in objects are merged and the last mentioned property wins, as you might expect.

Want to do both? Go for it. The first property may optionally be a function, followed by any number of objects.

var BrownBear = classic(Animal, bear, best);

Furthermore, you can do direct prototypal inheritance using classic.create:

var animal = { ... };
// Create a new animal, using animal object as the prototype.
var cheetah = classic.create(animal);
cheetah.run = function () { ... };

What's so great about Classic?

  • Tiny: you should save code weight with inheritance, not increase it.
  • Obvious: breaks down JavaScript inheritance into easy-to-understand steps.
  • Useful: exposes the useful bits of machinery, making it easier to work with objects and inheritance.
  • Efficient: uses prototypal inheritance and prototype chaining, leaves default objects alone. No black magic here.
  • JavaScript Objects are awesome!: Jeremy Ashenkas got it right with his classes-from-object-literals proposal. While we're waiting for the standards committee to figure things out, let's imitate what makes sense.

Browser support and testing

Should work everywhere. Also, Node and AMD script loaders are supported through classic.node.js and classic.amd.js.

You can run the unit tests by installing the dependencies (see below) and running make test.

Freebies

In addition to classic, you get a couple of free functions that are useful for working with objects:

classic.merge: merge any number of objects together:

var jazz = { genre: "jazz", composer: "Coltrain", duration: 103 };
var easyListening = { genre: "muzak", composer: "Some guy" };

classic.merge(jazz, easyListening, { composer: "Kenny G" });

Gives you:

{ genre: "muzak", duration: 103, composer: "Kenny G"}

classic.merge gives you a nice way to define static properties, too:

var Duck = classic(Bird, { ... });
classic.merge(Duck, {
   beakType: 'bill',
   footType: 'webbed'
});

classic.create: create a prototype chain between two objects. Delegates to Object.create, if supported.

Development

Unit tests use jasmine-node, which depends on Node.js and NPM. If you are developing on Mac OS X, an easy way to install Node and NPM is using Homebrew:

brew install node
brew install npm

Next, from the root directory of this repo, install the dependencies:

make install

You can also get some pretty documentation for the script:

make docs

If you plan on hacking the script, you can edit src/classic.js and then build the various versions automatically:

make all

This will create source and minified versions of all the files, as well as generating docs from the source.

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