jquery.stickem.js

/**
 * @name jQuery Stick 'em
 * @author Trevor Davis
 * @version 1.4
 *
 *	$('.container').stickem({
 *	 	item: '.stickem',
 *		container: '.stickem-container',
 *		stickClass: 'stickit',
 *		endStickClass: 'stickit-end',
 *		offset: 0,
 *		onStick: null,
 *		onUnstick: null
 *	});
 */

;(function($, window, document, undefined) {

	var Stickem = function(elem, options) {
		this.elem = elem;
		this.$elem = $(elem);
		this.options = options;
		this.metadata = this.$elem.data("stickem-options");
		this.$win = $(window);
	};

	Stickem.prototype = {
		defaults: {
			item: '.stickem',
			container: '.stickem-container',
			stickClass: 'stickit',
			endStickClass: 'stickit-end',
			offset: 0,
			start: 0,
			stickAlways: false,
			onStick: null,
			onUnstick: null
		},

		init: function() {
			var _self = this;

			//Merge options
			_self.config = $.extend({}, _self.defaults, _self.options, _self.metadata);

			_self.setWindowHeight();
			_self.getItems();
			_self.bindEvents();

			return _self;
		},

		bindEvents: function() {
			var _self = this;
			
			_self.$win.on('scroll.stickem', $.proxy(_self.handleScroll, _self));
			_self.$win.on('resize.stickem', $.proxy(_self.handleResize, _self));
		},

		destroy: function() {
			var _self = this;

			_self.$win.off('scroll.stickem');
			_self.$win.off('resize.stickem');
		},

		getItem: function(index, element) {
			var _self = this;
			var $this = $(element);
			var item = {
				$elem: $this,
				elemHeight: $this.height(),
				$container: $this.parents(_self.config.container),
				isStuck: false
			};

			//Stick always or if the element is smaller than the window
			if(_self.config.stickAlways || _self.windowHeight > item.elemHeight) {
				item.containerHeight = item.$container.outerHeight();
				item.containerInner = {
					border: {
						bottom: parseInt(item.$container.css('border-bottom'), 10) || 0,
						top: parseInt(item.$container.css('border-top'), 10) || 0
					},
					padding: {
						bottom: parseInt(item.$container.css('padding-bottom'), 10) || 0,
						top: parseInt(item.$container.css('padding-top'), 10) || 0
					}
				};

				item.containerInnerHeight = item.$container.height();
				item.containerStart = item.$container.offset().top - _self.config.offset + _self.config.start + item.containerInner.padding.top + item.containerInner.border.top;
				item.scrollFinish = item.containerStart - _self.config.start + (item.containerInnerHeight - item.elemHeight);

				//If the element is smaller than the container
				if(item.containerInnerHeight > item.elemHeight) {
					_self.items.push(item);
				}
			} else {
				item.$elem.removeClass(_self.config.stickClass + ' ' + _self.config.endStickClass);
			}
		},

		getItems: function() {
			var _self = this;

			_self.items = [];

			_self.$elem.find(_self.config.item).each($.proxy(_self.getItem, _self));
		},

		handleResize: function() {
			var _self = this;

			_self.getItems();
			_self.setWindowHeight();
		},

		handleScroll: function() {
			var _self = this;

			if(_self.items.length > 0) {
				var pos = _self.$win.scrollTop();

				for(var i = 0, len = _self.items.length; i < len; i++) {
					var item = _self.items[i];

					//If it's stuck, and we need to unstick it
					if(item.isStuck && (pos < item.containerStart || pos > item.scrollFinish)) {
						item.$elem.removeClass(_self.config.stickClass);

						//only at the bottom
						if(pos > item.scrollFinish) {
							item.$elem.addClass(_self.config.endStickClass);
						}

						item.isStuck = false;

						//if supplied fire the onUnstick callback
						if(_self.config.onUnstick) {
							_self.config.onUnstick(item);
						}

					//If we need to stick it
					} else if(item.isStuck === false && pos > item.containerStart && pos < item.scrollFinish) {
							item.$elem.removeClass(_self.config.endStickClass).addClass(_self.config.stickClass);
							item.isStuck = true;

							//if supplied fire the onStick callback
							if(_self.config.onStick) {
								_self.config.onStick(item);
							}
					}
				}
			}
		},

		setWindowHeight: function() {
			var _self = this;

			_self.windowHeight = _self.$win.height() - _self.config.offset;
		}
	};

	Stickem.defaults = Stickem.prototype.defaults;

	$.fn.stickem = function(options) {
		//Create a destroy method so that you can kill it and call it again.
		this.destroy = function() {
			this.each(function() {
				new Stickem(this, options).destroy();
			});
		};

		return this.each(function() {
			new Stickem(this, options).init();
		});
	};

})(jQuery, window , document);