Javascript多重继承模式

Question

I have used this pattern for inheritance in JS

MyApp.utils = {
    extend: function (subClass, baseClass, subClassMethods) {
        function inheritance() { }
        inheritance.prototype = baseClass.prototype;
        subClass.prototype = new inheritance();
        subClass.prototype.constructor = subClass;
        subClass.baseConstructor = baseClass;
        subClass.superClass = baseClass.prototype;

        if (subClassMethods == null) return;

        for (var index in subClassMethods) {
            subClass.prototype[index] = subClassMethods[index];
        }
    }
};

You use it like

MyApp.utils.extend(SubClass, BaseClass, {
    subMethodOne: function() {        
    }
});

This have worked nicely and the code is pretty straight forward, but it does not work with multiple inheritance because the constructor call will be to the subclass instead of baseclass and that will create a stack overflow

WHat is the best pattern for multiple inheritance? It must support prototype and that separate constructor logic in each class

JSFiddle: http://jsfiddle.net/HcPhL/1/ It will crash FF so beware :D

Answer 1

Inheritance in javascript is prototype based. This means objects inherit from each other and not classes. Instead of trying to use idioms from other programming languages you know I suggest you get to learn javascript's own idioms. I find using modules, cloning, and copying over functionality (since functions are objects), much more useful than classical inheritance in javascript.

That said, what you want to do could be accomplished the following way:

We want A to inherit from B and C sort of objects

1. Create a new object call it A
2. Iterate on each property of B (using a for... in loop) and assign it to A.
3. Iterate on each property of C (using a for... in loop) and assign it to A, here you may want to consider what is your take on conflict resolution (meaning whose methods, B or C you want to take precedence.

There are plenty of open source javascript libraries with an extend function, you can check the implementations there. Douglas Crockford also has a basic article on how to accomplish inheritance here and here is an article about javascript multiple inheritance

I'm assuming what you're trying to accomplish is code-reuse, I suggest you have a look at this free book by Addy Osmani learning javascript design patterns . Especially the module pattern.

Answer 2

Use mixins pattern or decorator patterns to support multiple inheritance. I could give you a detailed implementation if you need one