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Self — Python inspired class sugar! Build Status

Why another OOP abstraction?

Self is class-based sugar inspired from Python syntax that's perfect for continuation-passing style. No more var that = this;! The implicit this variable is changed to an explicit self variable that your inner functions inherit. Self plays nicely with existing prototypal, and Backbone OOP.

var Timer = Self(EventEmitter, {
    count: 0,
    constructor: function (self, interval) {;

        setInterval(function () {
        }, interval);
    tick: function (self) {
        self.count += 1;
        self.emit('tick', self.count);


Tested to work against Internet Explorer 6+, Safari 3+, Google Chrome 1+, Firefox 3+, and Opera 10+!

Development Version (1.0.0) — 6.5 KiB, uncompressed with comments.

Production Version (1.0.0) — 715 bytes, minified and gzipped.



To construct a base class, pass in a class definition to Self(...). The constructed class may be extended further by calling with <Class>.extend(...) method with a subclass definition. A class definition is an object containing properties and methods. Attached to every class is a __super__ property that points the parent class's prototype.

var Self = require('self');

var Animal = Self({

var Dog = Animal.extend({

var Beagle = Dog.extend({

Beagle.__super__ === Dog.prototype; // true

For JSLint compliance, a base class can be created using Self.extend(...).

var Animal = Self.extend({


The constructor for a class is the constructor method. Inside the constructor function, parent and mixin constructors can be called. The new keyword may be omitted when instantiating an object.

var Name = Self({
    name_prefix: 'Sir',
    constructor: function (self, name) {
        self._name = name;
    name: function (self, name) {
        if (typeof name !== 'undefined') {
            self._name = name;
        return self.name_prefix + ' ' +;

var NameAge = Name.extend({
    constructor: function (self, name, age) {, name);
        self.age = age;
    age: function (self, age) {
        if (typeof age !== 'undefined') {
            self._age = age;
        return self.age;

var name = new Name(),
    name_age = NameAge();

Static Properties

Static properties on a class will be inherited by the extending class. Except they're not prototypal, so any static defitions will be copied to the child class when extend is called. Defining a static property is as simple as setting a property on the class, or it can be done by using the sugar .staticProps method.

var Foo = Self({
    classMethod: function () {
        return 'ima class!';

var Bar = Foo.extend({

Bar.otherStaticMethod = function () {
    return 'ima static method on Bar!';


Mixins can be used for multiple inheritance. To mixin a object of properties (not a class), call <Class>.mixin(object). When mixing in, only properties not already in the existing class will be copied in.

var Foo = Self({
    _foo: 'foo',
    constructor: function (self) {
        console.log('Foo has been mixed in to: ' + + '!');
    foo: function (self, foo) {
        if (typeof foo !== 'undefined') {
            self._foo = foo;
        return self._foo;

var Bar = Self({
    constructor: function (self) {;



  • Self module

    • Self({Object} definition) — Shorthand for .extend({Object} definition).
    • Self({Object} prototype, {Object} definition) — Shorthand for .extend(Self.create({Object} prototype), {Object} definition).
    • .VERSION — Property indicating the version of Self.
    • .__super__ — Super prototype of Self, which is Object.prototype.
    • .extend({Object} definition) -> {Class} — Extends the class with a new class definition, returning the created class.
    • .mixin({Class}) — Copies another class's definitions into the Self base class.
    • .create({Constructor}) -> {Class} — Wraps a prototypal constructor as a Self class, returning the created class.
  • {Class} functor

    • Calling returns {Class Instance}, passing any arguments to the constructor method definition.
    • .__super__
    • .extend({Object} definition) -> {Class} — Same as above, extends the class, returning the created class.
    • .mixin({Class}) -> {Class} — Same as above, copies class definitions from mixin class into the current class. Returns the same class for chaining.
    • .staticProps({Object} definition) -> {Class} — Sugar method for defining static properties on a class.
  • {Class Instance} instantiated class object

    • Self does not add any extra methods aside from what was passed into the class definition.

Integrating With Other Forms of OOP

Prototypal OOP

A prototype can be manually wrapped with Self.create.

var EventEmitter = Self.create(require('events').EventEmitter);

Or use the shorthand and pass your base prototype as the first parameter in your class definition.

var Foobar = Self(EventEmitter, {
    constructor: function (self) {; // Calls EventEmitter's constructor


Backbone's initialize function is not the constructor. It's a call super method, which gets called by the real constructor. So as long as you keep the constructor semantics the same, you'll be fine!

var MyModel = Self(Backbone.Model, {
    initialize: function (self, attr, opts) {, attr, opts);


Since Self.js wraps every method with a function that unshifts the context onto your method's arguments, there is overhead. Yo u will have to weigh the performance impact vs the convenience of an explicit self variable.

For me, an empty Self method is 2 orders of magnitude slower than an empty prototypal method. Keep in mind this overhead may be negligible compared to the time it takes to run the code in your method. Below are the actual timings of calling those methods on my machine.

  • Without Self — 6 nanoseconds/call
  • With Self — 610 nanoseconds/call

To run these benchmarks yourself, clone this project and run: npm install -d && node ./benchmarks.js


It should be possible to macro Self methods in-place (only in Node.js), thus removing the overhead of wrapping every method. If anyone is interested in this, please let me know and we can investigate it!