///*回到顶部*/
        var layerFrom = ( document.compatMode.toLowerCase()=="css1compat" ) ? document.documentElement : document.body;
        function $(objID){return document.getElementById(objID);} 
		function doCompare() {
			var es = document.forms['compareForm'].elements;
			var n = 0;
			for (var i = 0; i < es.length; ++i) {
				var e = es[i];
				if (e.name == 'product_item_brand[]' && e.checked) { ++n; }
			}
			if(n < 2){alert("请至少选择两件商品进行对比");return false};
			if(n > 5){alert("最多选择五件商品进行对比");return false};
			document.forms['compareForm'].submit();
		}

		  function show_compare(id){
				var  spec_value=document.getElementById("spec_type_id").value;
				if(spec_value==""){
					spec_value=id
				}
				var es = document.forms['compareForm'].elements;
				var n = 0;
				var l = es.length;
				for (var i = 0; i < l; ++i) {
					var e = es[i];
					if (e.name == 'product_item_brand[]' && e.checked) { ++n; }
				}
				//alert(event.clientY+15);
				if (n > 0){				  
				  $("compare_layer").style.display='block';
				  $("compare_layer").style.top=layerFrom.scrollTop + event.clientY+10;
				  $("compare_layer").style.left=layerFrom.scrollLeft+ event.clientX-13;
			   }else{
				  $("compare_layer").style.display='none';
			   }
         }