JsMRO

Multiple inheritance for JS. Simple, but powerfull. Well tested. Inspired by the Python MRO C3 algorythm. (http://www.python.org/download/releases/2.3/mro/)

JsMRO provides:

• simple and easy to use interface,
• method resolution order identical to MRO C3,
• private members,
• do not interfere with JS this keyword,
• simple and short stacktraces form super methods.

To use JsMRO in your project just include inheritance.js and use global Class function to define your classes. See the examples below.

Examples

Simple cases

To define class call the Class function and pass constructor:

// This is empty class
var MyClass = Class(function(self, sup) {});

// Instantiate it
var myObject = new MyClass();

Constructor is one and only place to define your methods. You can also pass params when creating instance and initialize attributes.

var MyClass = Class(function(self, sup, myParam) {
    // Here comes initialisation:
    self.myAttr = myParam;
    self.myFunction = function() {
        return self.myAttr;
    };
});

var myObject = new MyClass(15);
// now myObject.myAttr == 15 and myObject.myFunction() returns 15

Inheritance

To inherite pass base-classes before constructor. Use sup to call super methods:

var MyBaseClass = Class(function(self, sup) {
    self.f = function() {
        return 'MyBaseClass';
    };
});

var MySubClass = Class(MyBaseClass, function(self, sup) {
    self.f = function() {
        // call super class function:
        var superValue = sup.f();
        return superValue + ' MySubClass';
    };
});

var o = new MySubClass();
// now o.f() returns 'MyBaseClass MySubClass'

Multiple inheritance

To inherite form more than one base classe pass all of them before constructor. Super-methods are called from left to right. To fully understand method resolution order (C3 MRO) read http://www.python.org/download/releases/2.3/mro/ .

var MyBaseClass = Class(function(self, sup) {
    self.f = function() {
        return 'MyBaseClass';
    };
});

var MyMixin = Class(function(self, sup) {
    self.f = function() {
        return 'MyMixin ' + sup.f();
    };
});

var MySubClass = Class(MyMixin, MyBaseClass, function(self, sup) {
    self.f = function() {
        return 'MySubClass ' + sup.f();
    };
});

var o = new MySubClass();
// now o.f() returns 'MySubClass MyMixin MyBaseClass'

Initializers

Initializer is a __init__ method. It is called just after the object has been constructed and with the same parameters the constructor has been called. Since object has allready been constructed, inside __init__ you can do everything you can do in any other method, including calling super and other methods.

var MyClass = Class(function(self, sup) {
    self.__init__ = function(param) {
        self.param = param;
    };
});

var o = new MyClass('value');
// now o.param == 'value'

Private members

You can simply create private members with var keyword:

var MyClass = Class(function(self, sup) {
    var myPrivateCounter = 0;
    
    self.getCounter = function() {
        myPrivateCounter += 1;
        return myPrivateCounter;
    };
});

In the similar way you can create private functions.

Full API

Function Class

Class(baseClasses..., function(self, sup, args...) { // constructor body }) - returns new class. Takes base classes and a constructor function as an argument. Inside constructor function self is current object, sup is super object and args is argument list. Returns new class that inherits from 'baseClasses' and is constructed with constructor function.

To instantiate class use new keyword on class: o = new C(args...);. At first constructor functions are invoked on classes bottom-up to construct the object. When object is fully constructed and it has __init__ method, it is called with initial arguments.

Use __init__ method to initialize your object using MRO.

Function isInstance

isInstance(obj, cls) function checks if object obj is instance of class cls.

Function isSubclass

isSubclass(sub, sup) function checks if class sub is subclass of class sup or equal.

Other notes

JsMRO use __class__ attribute on your objects and __mro__, __id__ and __initializer__ on classes. Do not use them, or you 'll mess everything up.

Do not define your methods anywhere outside constructor.

TESTS

To run tests download whole project and visit tests.html with you browser. Current version has been tested with Chrome 24, FireFox 20 and IE 9.