How can I extend properly a JS object?

Question

Let's say I have something like this in a file named main.js:

function obj_name() {}

obj_name.prototype = {
    foo  : function() { alert('hi!'); },
    foo2 : function() { alert('hi again!'); }
}

Now I am trying this way to expand the object in another file extend.js:

obj_name.prototype = {
    newfoo : function() { alert('hi #3'); }
}

... but the problem is that it will just work if I code it this way:

obj_name.prototype.newfoo = function() { alert('hi #3'); }

I guess this may be a noob question. I don't even know if this is the proper way to extend an object, but I am freaking out here wondering why does this happen.

Thank you guys in advance.

Answer 1

Another option without jQuery:

var extend = function(destination, source)
{
    for (var property in source)
    {
        if (destination[property] && (typeof(destination[property]) == 'object')
                && (destination[property].toString() == '[object Object]') && source[property])
            extend(destination[property], source[property]);
        else
            destination[property] = source[property];
    }
    return destination;
}

var a = {a: 'test'};                              // original
var b = {newFoo: function() { alert('hi #3'); }}; // the addition
extend(a, b);                                 // extend it
a.newFoo();                                   // call the added property