Webkit browsers, especially in Mac OSX, hide the scrollbar intelligently when not in use. This feature improves the look and feel of the browser. But for the designers, sometimes this can be a pain because they may need to alter the design based on the visibility of the scrollbar.

Here are two simple jQuery plugins that can detect the visibility of the scrollbar for a given DOM element:

For Horizontal Scrollbars

(function($) {
	$.fn.hasHorizontalScrollBar = function() {
		return this.get(0) ? this.get(0).scrollWidth > this.innerWidth() : false;
	}
})(jQuery);

For Vertical Scrollbars

(function($) {
	$.fn.hasVerticalScrollBar = function() {
		return this.get(0) ? this.get(0).scrollHeight > this.innerheight() : false;
	}
})(jQuery);

You can use it like this:

if($("#element").hasVerticalScrollbar()){
	//do whatever you'd like to
}

Source and idea: this StackOverflow discussion.