一种简单实用的JS实现页面加载完毕之前loading提示效果，做成js调用即可：

<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:1;filter:alpha(opacity=80);z-index:10000;"><div style="position: absolute; cursor1: wait; left: ' + loadingLeft + 'px; top:' + loadingTop + 'px; width: auto; height: 57px; line-height: 57px; padding-left: 50px; padding-right: 5px; background: #fff url(Image/loading.gif) no-repeat scroll 5px 10px; border: 2px solid #95B8E7; color: #696969; font-family:\'Microsoft YaHei\';">页面加载中，请等待...</div></div>';
    document.documentElement.style.overflowY = 'hidden';
    document.write(loadingHtml);
    document.onreadystatechange = completeLoading;

    function completeLoading() {
        if (document.readyState == "complete") {
            var loadingMask = document.getElementById('loadingDiv');
            loadingMask.parentNode.removeChild(loadingMask);
            document.documentElement.style.overflowY = 'scroll';
        }
    }
</script>

说明：

将此段js代码放入head最后即可；

其中loading效果的样式可以根据自己的风格修改，loading.gif图片可自行搜索下载。