Window.TWTR undefined


I want to make sure that the widget.js is not included twice, so I am doing something like this in my code
(window.TWTR)|| document.write(’<script src ="//"’);
And it is not even behaving properly,

so, i want to see where the problems is , i just simply did

And the alert prompt says “undefined”,

I tested on Chrome, IE, Firefox.

So, that means I cannot really leverage the window.TWTR object to check if the widget.js has been loaded right? any work around for this?