Question

var Blah = Blah || {};

or

if ((typeof Blah) == 'undefined') {
  var Blah = {};
}

Is there a difference or both do the same thing?

Answer 1

There is a difference. The first assigns Blah to Blah, but if Blah is a falsy value (one which typecasts to false in a boolean context, such as NaN, undefined, 0 and ''), it’ll set Blah to an empty object.

The second only sets Blah to an empty object if it is exactly undefined, as the only value with the typeof type undefined is undefined.

Also, you are creating just objects, not namespaces. Even the concept of namespaces in JavaScript is iffy at best; most of the time it is done by creating a self-calling anonymous function that exports some things into a global object and not others.