js实现页面加载动画

    //获取浏览器页面可见高度和宽度
var _PageHeight = document.documentElement.clientHeight,
    _PageWidth = document.documentElement.clientWidth;
//计算loading框距离顶部和左部的距离（loading框的宽度为215px，高度为61px）
var _LoadingTop = _PageHeight > 61 ? (_PageHeight - 61) / 2 : 0,
    _LoadingLeft = _PageWidth > 215 ? (_PageWidth - 215) / 2 : 0;
//在页面未加载完毕之前显示的loading Html自定义内容
var _LoadingHtml = '
'px;top:0;background:#f3f8ff;opacity:1;filter:alpha(opacity=80);z-index:10000;">
'px; top:' + _LoadingTop + 'px; width: auto; height: 57px; line-height: 57px; padding-left: 50px; padding-right: 5px; background: #fff url(images/uploading.gif) no-repeat scroll 5px 10px; border: 2px solid #95B8E7; color: #696969; font-family:\'Microsoft YaHei\';">正在处理...请等待...
';
//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);
}
}