What does this Javascript code mean? [duplicate]

Question

Possible Duplicate:
What does “options = options || {}” mean in Javascript?

Looking at the YouTube source...

var yt = yt || {};

Does that mean.. set yt to yt if yt exists, else create a new object?

If that's the case, I didn't think you can put a condition when declaring a variable.

Answer 1

Assign the value of yt back to yt unless it is any of 0, NaN, false, null, "", or undefined (i.e. it's falsy), in which case assign {} to yt.

This works because each of the values in the list above evaluate to false in a boolean expression.

Answer 2

It means exactly that: If the content does not evaluate to false, assign it to itself (which is a neutral operation), otherwise create a new object and assign it to yt. It's typically used to instantiate objects to use as namespaces, first checking if the namespace already exists.