jclass

jclass started as a port of John Resig's lightweight OO inheritance model. However, this implementation is faster as it avoids threefold method wrapping (see here). In addition, it provides class members, property descriptors, conversion of prototype-based classes and various conveniences.

jclass has no dependencies and works in most import environments: RequireJS (AMD), CommonJS, NodeJs and web browsers.

Note: The current version (1.X.X) is a merge of the node-oo project and the previous version of jclass (0.2.X). For legacy code, see the v0.2.X branch.

Installation

jclass is hosted at npmjs. Install it via:

npm install jclass

Examples

All examples below use NodeJs but the jclass related code would also work in other environments.

Simple Inheritance

var Class = require("jclass");

var Cat = Class._extend({

  // constructor
  init: function(color) {
    this.color = color;
  },

  // instance method
  meow: function() {
    console.log("An abstract cat cannot meow!");
  },
  
  // instance method
  getColor: function() {
    return this.color;
  }

});


var GrumpyCat = Cat._extend({

  // constructor
  init: function init() {
    init._super.call(this, "greyish");
    
    // if you don't want to use a named function you can also use
    // this.init._super.call(this, "greyish");
  },

  // instance method
  meow: function() {
    console.log("Nah, not in the mood.");
  }

});

var cat = new Cat("black");
cat.meow(); // "An abstract cat cannot meow!"

var grumpy = new GrumpyCat();
grumpy.meow(); // "Nah, not in the mood."
grumpy.getColor(); // "greyish", same as grumpy.color

// instanceof works as expected
console.log(grumpy instanceof GrumpyCat); // true
console.log(grumpy instanceof Cat); // true
console.log(GrumpyCat._extends(Cat)); // true, same as GrumpyCat._superClass == Cat
console.log(GrumpyCat._extends(Class)); // true

Class members

Class members are accessible via the _members property which is itself a jclass instance. To add class members, add a second paramter to _extend.

var Class = require("jclass");

var Cat = Class._extend({
  // instance members

  // constructor
  init: function(color) {
    this.color = color;
  },

  // instance method
  meow: function() {
    console.log("An abstract cat cannot meow!");
  }

}, {
  // class members

  family: "Felidae",

  getFamily: function() {
    console.log(this.family);
    // same as
    // console.log(Cat._members.family);
  }

});

Cat._members.getFamily()); // "Felidae", same as Cat._members.family

Please note that this within class methods references the _members instance itself.

Property Descriptors

All instance and class members given to _extend can also be applied as property descriptors that are passed to Object.defineProperty. All you need to do is define members as objects and add a property descriptor: true. Both, accessor-type and data-type descriptors are supported.

var Class = require("jclass");

var MyClass = Class._extend({

  someKey: {
    descriptor: true,
    get: function() {
      return "some value";
    }
  }

});

var myInstance = new MyClass();
console.log(myInstance.someKey); // "some value"

Converting Prototyped Classes

You can convert prototype-base classes into jclasses.

// example using nodejs

var Class        = require("jclass");
var EventEmitter = require("events").EventEmitter;

var Emitter = Class._convert(EventEmitter);

var emitter = new Emitter();
emitter.on("topic", function() { ... });
emitter.emit("topic", ...);
});

The instance of the (original) prototyped class is stored as _prototype in each jclass instance.

API

Classes

Classes have the following attributes:

• _extend (function(instanceMembers, classMembers)): Derives a new class with instanceMembers and classMembers (example).
• _extends (function(Class)): Returns true (false) if Class is (is not) a super class.
• _superClass (Class): The super class (not available for the base Class).
• _subClasses (array): An array containing all (directly inheriting) sub classes.
• _members (Class instance): A jclass instance that handles the class members (example).

The base Class has additional attributes that are not propagated to derived classes:

• _convert (Function(cls, options)): Converts a prototype based class cls into a jclass (example).
• _construct (Function(cls, args)): Returns an instance of cls, instantiated with args. This is an apply-like usage for new.

Instances

All instances have the following attributes:

• _class (Class): The class of this instance

Within instance methods, the super method is always referenced as _super.

If the option exposeClassMembers is true, each instance can directly access class members within instance methods. You can use the _class attribute outside of instance methods or if exposeClassMembers is false.

Development

• Source hosted at GitHub
• npm module hosted at npmjs
• Report issues, questions, feature requests on GitHub Issues

Authors

Marcel R. (riga)