prototypal inheritance done right

Usage no npm install needed!

<script type="module">
  import prototypal from '';



build status

Mit Style License

Where is Class ?

The initial Class module has been actually merged in this namespace where available.

Right now you can find more info about Class on this page


All utilities in this namespace should work with every JavaScript engine, down to IE6, Opera Mini, duktape, nodejs, and all others.

How / Which File

npm install prototypal then var create = require('prototypal').create

Same is for bower install prototypal AMD module, however needed files are:

This package is registered in bower too.

prototypal.create(extend[, properties])

The API is very similar to the one proposed in lo-dash except it promotes instead of copying over the properties object whenever is possible (for better performance)

// a null object example
var n = prototypal.create(null);

// a generic inherited example
var a = {
      testa: 123
    b = create(a, {
      testb: 456

a.hasOwnProperty('testa'); // true
b.hasOwnProperty('testa'); // false
b.hasOwnProperty('testb'); // true
b.testa; // 123
b.testb; // 456

prototypal.Class(extend[, prototype])

Similar to prototypal.create, Class aim is to define reusable prototypes.

var Class = prototypal.Class;

var Null = Class(null, {
  // some optional method
  // that we might want to inherit

var n = new Null;
n instanceof Object; // false

The signature accepts a single argument as function, where its prototype will be used as inheritance chain, or an object to extend or a prototype.

var Rectangle = Class({
  constructor: function (width, height) {
    this.width = width;
    this.height = height;
  toString: function () {
    return '[object Rectangle]';
  area: function () {
    return this.width * this.height;

var Square = Class(Rectangle, {
  constructor: function (size) {, size, size);
  toString: function () {
    return '[object Square]';

var s = new Square(3);
s.area(); // 9
'' + s;   // [object Square]

prototypal.Class(extend[, function])

If the second argument is a function, it will be invoked with the extended parent/super passed as argument. In such case, the function needs to return descriptors.

var Rectangle = Class({
  constructor: function (width, height) {
    this.width = width;
    this.height = height;

var Square = Class(Rectangle, function (parent) {
  // a closure with fast and private parent/super access
  // *must* return the descriptors object
  return {
    constructor: function (size) {
        this, size, size

ES5 prototypal.Class(extend[, prototype])

For JavaScript engines already compatible with ES5, the Class is the one proposed initially with Class.lazy, Class.descriptor, and Class.bound.

General Compatibility

Methods such prototypal.copy(), prototypal.create(), and prototypal.keys() are compatible with all JavaScript and JScript engines, down to Internet Explorer version 6, including Opera Mini and other server side based browsers.

You can test directly online if your browser is supported, including IE6.

However, while prototypal.Class is tested everywhere too, in those browsers where ES5 is available it behaves in a more powerful way (so if these are your browsers targets, just use all extra features such Class.lazy, Class.descriptor, or Class.bound).

All these platforms have been tested against the more powerful ES5 Class and its extra features:

  • iOS 5.1 or greater
  • Android 2.2 or greater
  • webOS 2.2 or greater
  • Kindle Fire Silk 3 or greater
  • Windows Phone 7 (IE9 Mobile) or greater
  • BlackBerry 10 or greater
  • Nokia Xpress on WP and Asha 11 or greater
  • Samsung Bada
  • Opera Mini and Opera Mini J2ME
  • FirefoxOS 1.0 or greater
  • Desktop IE9, Chrome, Opera, Safari, Midori, others
  • UC Browser and UC Browser Mini

On the server side, nashorn, duktape, nodejs, and Rhino work as expected too, as well as any other JavaScript server side engine probably should.

If you find any platform that is not green please file a bug and/or let me know, thank you.