获取是否有滚动条

var isScroll = function (el) {
                 // test targets
                 var elems = el ? [el] : [document.documentElement, document.body];
                 var scrollX = false, scrollY = false;
                 for (var i = 0; i < elems.length; i++) {
                     var o = elems[i];
                     // test horizontal
                     var sl = o.scrollLeft;
                     o.scrollLeft += (sl > 0) ? -1 : 1;
                     o.scrollLeft !== sl && (scrollX = scrollX || true);
                     o.scrollLeft = sl;
                     // test vertical
                     var st = o.scrollTop;
                     o.scrollTop += (st > 0) ? -1 : 1;
                     o.scrollTop !== st && (scrollY = scrollY || true);
                     o.scrollTop = st;
                 }
                 // ret
                 return {
                     scrollX: scrollX,
                     scrollY: scrollY
                 };
             };