Self—Python inspired class sugar!

Downloads – Documentation – API – Integrating – Performance

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) {
        Timer.__super__.constructor.call(self);

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

Downloads

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.

Documentation

Inheritance

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({
});

Constructors

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 + ' ' + self.name;
    }
});

var NameAge = Name.extend({
    constructor: function (self, name, age) {
        NameAge.__super__.constructor.call(self, 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 definitions 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({
}).staticProps({
    classMethod: function () {
        return 'ima class!';
    }
});

var Bar = Foo.extend({
});

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

Mixin

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: ' + self.name + '!');
    },
    foo: function (self, foo) {
        if (typeof foo !== 'undefined') {
            self._foo = foo;
        }
        return self._foo;
    }
});

var Bar = Self({
    constructor: function (self) {
        Foo.call(self);
    }
});

Bar.mixin(Foo);

API

Module

var Class = Self(definition)

var Class = Self.extend(definition)

Creates a new class. Self() is shorthand for Self.extend().

var Class = Self(prototype, definition)

Shorthand for Self.extend(Self.create(prototype), definition).

var Class = Self.create(prototype)

Wraps a prototypal constructor as a Self class, returning the created class.

Self.VERSION

Property indicating the version of Self.

---

Class static methods & properties

var inst = Class(args...)

Calling returns an instance of the class, passing any arguments to the constructor method.

var Child = Class.extend(definition)

Extends the class with a new class definition, returning the created class.

Class.staticProps(definition) === Class

Sugar method for defining static properties on a class.

Class.mixin(AnotherClass) === Class

Copies another class's definitions into the current class.

Class.__super__

Parent class

---

Instance properties

inst.__class__

The class that created this instance.

inst.__super__

The parent class of this instance, same as inst.__class__.__super__.

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) {
        Foobar.__super__.constructor.call(self); // Calls EventEmitter's constructor
    }
});

Backbone

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) {
        MyModel.__super__.initialize.call(self, attr, opts);
    }
});

I recommend extending the Backbone library into your own namespace, so you don't have to call Self on the library everytime. It also provides a place for you to roll your own base class logic.

var mvc = _.reduce(Backbone, function (obj, value, key) {
    obj[key] = (value.prototype && _.keys(value.prototype).length) ? Self.create(value) : value;
    return obj;
}, {});

mvc.Collection = mvc.Collection.extend({
});

Performance

Since Self.js wraps every method with a function that unshifts the context onto your method's arguments, there is overhead. You 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

Thoughts

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!