进度条显示—正在加载中......

1.在ajax中调用：
beforeSend:function(XHR){
     $("#loading").show();
  },这个方法

返回success时设置为隐藏即可：$("#loading").hide();

2.显示层
<div id="loading" style="z-index:99999;display:none; position:fixed; top:0;left:0; width:100%;
height:100%;background-image:url(images/loading.gif); background-position:center;
background-repeat:no-repeat; text-align:center;">
<div style="position:absolute; top:42%; left:45%; width:10%; text-align:center;">正在提交数据，请稍候……</div>
</div>

3.图片loading.gif
<img src="http://img.blog.csdn.net/20151119143937319?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" height="45" width="45" alt="" />