Extends a object method with a function, requires underscore.js

extendmethod.js

var obj = {
    init: function() {
        console.log("init old");
    }
};

var old_obj = {};

_.extend(old_obj, obj);

console.log("'old' init():");
obj.init();

obj.init = function() {
    old_obj.init.apply(this);
    console.log("init extensions");
};

console.log("extended init():");
obj.init();