页面加载时

    <script type="text/javascript">
        var _PageHeight = document.documentElement.clientHeight,
            _PageWidth = document.documentElement.clientWidth;
        var _LoadingTop = _PageHeight > 61 ? (_PageHeight - 61) / 2 : 0,
            _LoadingLeft = _PageWidth > 215 ? (_PageWidth - 215) / 2 : 0;
        var _LoadingHtml = '<div id="loadingDiv" style="position:absolute;left:0;width:100%;height:' + _PageHeight + 'px;top:0;background:#f3f8ff;opacity:0.8;filter:alpha(opacity=80);z-index:10000;"><div style="position: absolute; cursor1: wait; left: ' + _LoadingLeft + 'px; top:' + _LoadingTop + 'px; width: auto; height: 45px; line-height: 45px; padding-left: 40px; padding-right: 5px; background: #fff url(../Images/loading.gif) no-repeat scroll 5px 10px; border: 1px solid #95B8E7; color: #696969; font-family:\'Microsoft YaHei\';">页面加载中...</div></div>';
 
        window.onload = function () {
            var a = document.getElementById("loadingDiv");
            a.parentNode.removeChild(a);
        }
        //呈现loading效果
        document.write(_LoadingHtml);

        ////监听加载状态改变
        //document.onreadystatechange = completeLoading();

        ////加载状态为complete时移除loading效果
        //function completeLoading() {
        //    if (document.readyState == "complete") {
        //        var loadingMask = document.getElementById('loadingDiv');
        //        loadingMask.parentNode.removeChild(loadingMask);
        //    }
        //}
    </script>