Question

i know how to do inheritance in javascript but i can only inherit a single object.
eg.

function fun1() {
this.var1=10;
this.meth1=function() {
...
...
};
}

function fun2() {
this.var2=20;
this.meth2=function() {
...
...
};
}

function fun3() {
this.var3=30;
this.meth3=function() {
...
...
};
}

now if i want an fun3 object to inherit fun1 object i can do this

fun3.prototype=new fun1();

or to inherit fun2 object i can do this

fun3.prototype=new fun2();

but how can i inherit both fun1 and fun2?

Answer 1

Technically, JavaScript does not offer multiple inheritance. Each object has a well-defined single “prototype” object, and thus a “prototype chain”.

However, it is possible to augment any object with additional methods, so-called “expandos”. So you could iterate over a collection of methods and individually add them to newly created objects. Such a collection is called “mixin”.

Several frameworks offer mixins, for example:

• qooxdoo
• ExtJS
• mootools
• …

They all work pretty much the same.

Note however that this is not real inheritance, since changes to the mixin will not be reflected in the objects.

For example:

var mixin = {
    method: function () {
        console.log('Hello world!');
    }
};
var foo = new fun1();
foo.method = mixin.method;
foo.method(); // Hello world!
mixin.method = function () { console.log('I changed!') };
foo.method(); // Hello world!