Yes, it looks like you’re correct. In this case, probably the easiest thing to do would be to just check the existence of MY.CUSTOM before calling MY.CUSTOM.namespace().

More importantly, I hope the benefits of using some of these techniques was made clear enough. But thanks for spotting that.

I like creating closures this way (without the need to perform a ‘new’ to the existing object):

var myObject = function() {
var newValue = this.property1;
return {
property1 : ‘value1′;
property2 : ‘value2′;
performMethod : function() {
var myMethodValue = newValue;
return myMethodValue;
};
}
}

if (typeof MY == “undefined”) {
MY = new Object();
MY.CUSTOM = new Object();
}

If MY is defined, but MY.CUSTOM isn’t, then the next assignment should fail:

MY.CUSTOM.namespace = function() {

This would seem like a nitpick, but this would be exactly
the case if you have a set of several JS files in one namespace, and one of them has been included ahead of MY.CUSTOM.

FWIW, the idiom Dustin Diaz uses for this check looks cleaner to me:

var DED = window.DED || {};

http://www.dustindiaz.com/javascript-private-public-privileged/

As Crockford points out, you shouldn’t need to do
“new Object()”, you can just assign an object literal
with {}, or even start populating it straight away:

if (typeof MY.CUSTOM === “undefined”)
{
MY.CUSTOM = {
namespace : function() { … }
};
}

adéu,
Mateu