Makes more sense to me to have the "Tweet" button enabled by default and disabled on load by JS. If there's an issue with the JS or it's disabled in the browser or whatever, the button should still work (with server side logic to catch empty Tweets). Right now, if the JS doesn't load you can't Tweet at all.

Just a small nitpick I had after thinking about the reasoning behind why the OP had disabled the button in JS rather than the HTML in the first place.