js onloading 效果

//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);
    }
}

function onLoading(){
    console.log("test onLoading...");
    //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 = '<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>';
    //呈现loading效果
    document.write(_LoadingHtml);

    //window.onload = function () {
//      var loadingMask = document.getElementById('loadingDiv');
//      loadingMask.parentNode.removeChild(loadingMask);
    //};

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

2.在Ajax中调用即可

var strURL = "loginServlet?loginId="+loginId+"&password="+password;
   var self = this;
      if (window.XMLHttpRequest) {
          self.xmlHttpReq = new XMLHttpRequest();
      }
      else if (window.ActiveXObject) {
          self.xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
      }
      
     
      
      self.xmlHttpReq.open('GET', strURL, true);
      self.xmlHttpReq.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
      self.xmlHttpReq.onreadystatechange = function() {
          if (self.xmlHttpReq.readyState == 4 ) {
            if(self.xmlHttpReq.status==200){
              var result = self.xmlHttpReq.responseText;
              var a="OK";
              if (result==a){
                onLoading();//here to use
                window.location.href=responseURL;
              }else{
                responseMsg.innerHTML = result;
              }
              
            }else{
          alert('Ajax Request Error.');
        }
          }
      
      }
      self.xmlHttpReq.send(null);

参考：

​​http://qubernet.blog.163.com/blog/static/1779472842014510392573/​​