Self — Python inspired class sugar!
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 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({
}).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
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);
}
});
Performance
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
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!