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Simple functions for extending JavaScript objects


Provides two simple methods for working with inheritance and objects. This library is heavily influenced by the simplistic prototypal inheritance provided in both CoffeeScript and Backbone and simply exists so that it can be included in other libraries.

inherit(Parent, methods, properties)

Creates a new constructor function that inherits from a parent constructor. Instance and static methods can also be provided as additional arguments, if the methods argument has a property called constructor this will be used as the constructor function.


  • parent: A constructor Function to inherit from.
  • methods: An Object literal of instance methods that are added to the constructors prototype (optional).
  • properties - An Object literal of static/class methods to add to the constructor itself (optional).


// Original function to inherit from. 
function MyObject() {};
var SubClass = inherit(MyObject, {
  instanceMethod: function () {}
}, {
  staticProp: 'some-string',
  staticMethod: function () {}
var instance = new SubClass();
instance instanceof MyObject   //=> true 
typeof instance.instanceMethod //=> "function" 
typeof SubClass.staticMethod   //=> "function" 

A __super__ property is made available to all child classes that points to the parent prototype object. This can be used in methods to call the parent.

// Original function to inherit from. 
function MyObject() {};
MyObject.prototype.say = function () { return 'Hello'; }
var SubClass = inherit(MyObject, {
  constructor: function SubClass() {
    SubClass.__super__.constructor.apply(this, arguments);
    // Set up other properties. 
  say: function () {
    return SubClass.__super__.say.apply(this, arguments) + ' World';
(new SubClass()).say(); //=> 'Hello World' 

mixin(target [ , arguments... ])

Extends an object with the properties on successive arguments. Returns the first argument. Properties will be copied from right to left with the right overriding the left.


  • target: The object that is to be extended.
  • arguments*: Properties from all successive arguments will be copied to the target.


mixin({type: 'person'}, {name: 'bill', age: 20}, {age: 21});
//=> {type: 'person', name: 'bill', age: 21} 


Creates a new object instance and sets it's internal prototype to the parent argument provided. This is based on Crockford's Object.create() but will use the native Object.create() if present. Unlike Object.create() this function will always return a new object even if a non object is provided as an argument.


  • parent: An object to use for the new objects internal prototype.


var appleObject = {color: 'green'}
var appleInstance = create(appleObject);
appleInstance.hasOwnProperty('color'); //=> false 
appleInstance.color === appleObject.color; //=> true 


Tests require Node and Vows to run. To install Vows using npm run:

$ npm install vows

Then to run the tests simply enter:

$ vows inheritance-test.js


Released under the MIT license