http://jsfiddle.net/handtrix/sbwL7/

gistfile1.txt

<div data-display-viewport="500" class="reorder-elements">
  <div data-display-order="99">99</div>
  <div data-display-order="999">999</div>
  <div data-display-order="12">12</div>
  <div data-display-order="11">11</div>
  <div data-display-order="10">10</div>
  <div data-display-order="9">9</div>
  <div data-display-order="3">3</div>
  <div data-display-order="2">2</div>
  <div data-display-order="1">1</div>
  <div data-display-order="9999">9999</div>
</div>

Order HTML elements based on viewport

(function($) {

	function OrderedNode(element) {
		this.$element = $(element);
		this.maxViewport = parseInt(this.$element.data(this.maxViewportName));
		this.saveOldState();
		this.decide();
		
		if (this.maxViewport) {
			// Todo: Throttle
			$(window).resize($.proxy(this.decide, this));
		}
	}

	OrderedNode.prototype = {
		dataAttrName: 	 'display-order',
		dataAttrBkpName: 'display-order-backup',
		maxViewportName: 'display-viewport',

		saveOldState: function(){
			var _this = this;
			this.$element
				.children()
				.each(function(index, element){
					$(this).data(_this.dataAttrBkpName, index);
				});
		},

		decide: function() {
			if (!this.maxViewport) {
				// Reorder
				return this.order(true);
			} else if (this.maxViewport >= window.innerWidth) {
				// Reorder
				return this.order(true);
			} else {
				// Undo Reorder
				this.order(false);
			}
		},

		order: function(newState) {
			var dataAttrName = newState ? this.dataAttrName : this.dataAttrBkpName;
			var i = 0;

			// Detach and Sort Elements
			var sorted = this.$element
				.children()
				.detach()
				.sort(function(a, b) {
					console.log('sort', dataAttrName);

					a = parseInt($(a).data(dataAttrName), 10);
					b = parseInt($(b).data(dataAttrName), 10);

					++i;

					if (a > b) {
						return 1;
					} else if (a < b) {
						return -1;
					} else {
						return 0;
					}
				});

			// Retach newly sorted Elements
			this.$element.append(sorted);
		}
	}

	$('.reorder-elements').each(function(index, element) {
		new OrderedNode(element);
	})

})($ || jQuery);