Super simple Character Limit checker in Javascript

char_limit.js

// Check character count and limit input field
// -------------------------------------------
// Original from: http://www.9lessons.info/2010/04/live-character-count-meter-with-jquery.html
//
$("#tweetBox").on('keyup',function()
{
	var box=$(this).val();
	var limit= 140 
	var count= limit - box.length;

	if(count >= 0)
	{
		$('#count').html(count);
	}
	else
	{
		// truncate
		$(this).val(box.substring(0,limit));
	}
	return false;
});