jquery.smoothscroll.js

/*! http://mths.be/smoothscroll v1.5.2 by @mathias */
;(function(document, $) {

	var $scrollElement = (function() {
	    // Find out what to scroll (html or body)
	    	var $html = $(document.documentElement),
	    	    $body = $(document.body),
	    	    bodyScrollTop;
	    	if ($html.scrollTop()) {
	    		return $html;
	    	} else {
	    		bodyScrollTop = $body.scrollTop();
	    		// If scrolling the body doesn’t do anything
	    		if ($body.scrollTop(bodyScrollTop + 1).scrollTop() == bodyScrollTop) {
	    			return $html;
	    		} else {
	    			// We actually scrolled, so undo it
	    			return $body.scrollTop(bodyScrollTop);
	    		}
	    	}
	    }());

	$.fn.smoothScroll = function(speed) {
		speed = ~~speed || 400;
		// Look for links to anchors (on any page)
		return this.find('a[href*="#"]').click(function(event) {
			var hash = this.hash,
			    $hash = $(hash); // The in-document element the link points to
			// If it’s a link to an anchor in the same document
			if (location.pathname.replace(/^\//, '') === this.pathname.replace(/^\//, '') && location.hostname === this.hostname) {
				// If the anchor actually exists…
				if ($hash.length) {
					// …don’t jump to the link right away…
					event.preventDefault();
					// …and smoothly scroll to it
					$scrollElement.stop().animate({ 'scrollTop': $hash.offset().top }, speed, function() {
						location.hash = hash;
					});
				}
			}
		}).end();
	};

}(document, jQuery));