ajax异步加载遮罩层特效

<!doctype html>
<html>
<head>
<title>遮罩层（正在加载中）</title>
<meta charset="utf-8" />
<style>
#cover{
display:none;
position:fixed;
z-index:1;
top:0;
left:0;
width:100%;
height:100%;
background:rgba(0, 0, 0, 0.44);
}
#coverShow{
display:none;
position:fixed;
z-index:2;
top:50%;
left:50%;
border:1px solid #127386;
width:300px;
height:100px;
margin-left:-150px;
margin-top:-150px;
background:#127386;
}
</style>
<script>
function coverit() {
    var cover = document.getElementById("cover");
    var covershow = document.getElementById("coverShow");
    cover.style.display = 'block';
    covershow.style.display = 'block';
} 

function hidden_coverit() {
    var cover = document.getElementById("cover");
    var covershow = document.getElementById("coverShow");
    cover.style.display = 'none';
    covershow.style.display = 'none';
}
</script>
</head>
<body>
<div id="cover"></div>
<div id="coverShow">
<table align="center" border="0" width="100%" cellspacing="0" cellpadding="0" style="border-collapse: collapse; height: 100px; min-height: 100px;" bgcolor="#127386">
<tr>
<td height="30" style="font-size: 12px;">数据加载中，请稍后......</td>
</tr>
<tr>
<td align="center" bgcolor="#ffffff">
<img src="./20141023034634293.gif" alt="" />
</td>
</tr>
</table>
</div> 

<input type="button" value="遮住" onclick="coverit()"/>
</body>
<script type="text/javascript">
            coverit();//开始加载遮罩层（正在加载中...）
            $.ajax( {
                url:'/StatisticsGame/OverallSituationDo',
                data:{
                    new_start_time:new_start_time,//开始时间
                    new_end_time:new_end_time,//结束时间
                    req_game:$("#select_game1").select().val(),
                    get_select_platform:$('#select_platform').val(),
                    req_mode:search_mode},
                type:'post',
                cache:false,
                async:true,
                dataType:'json',
                success:function(data) {
                    $(".asset_table_tr").remove();
                    $('.add_tpl_view').remove();
                    if(data["req"] == "success"){
                        hidden_coverit();//得到数据之后，关闭遮罩加载中...
                        var total_new_count = 0;
                        var total_new_incom_moneys=0;
                        var total_new_draw_moneys=0;
                        var total_get_incom_total_moneys=0;
                        var total_get_draw_total_moneys=0;
                        var total_total_assets_moneys=0;
                        var total_login_count=0;
                        for(i = 0; i < data["data"].length; ++i){

                            var date = data["data"][i]["new_time"];//日期
                            var get_select_platform = data["data"][i]["select_platform_name"];//平台名称
                            var login_count =Number(data["data"][i]["count"]);//登录用户数
                            var new_count =Number(data["data"][i]["new_count"]);//新用户数
                            var new_incom_moneys =Number(data["data"][i]["new_incom_money"]);//转入资金用户
                            var new_draw_moneys =Number(data["data"][i]["new_draw_money"]);//转出资金用户
                            var get_incom_total_moneys =Number(data["data"][i]["total_incom_money"]);//转入资金总额
                            var get_draw_total_moneys =Number(data["data"][i]["total_draw_money"]);//转出资金总额
                            var total_assets_moneys =Number(data["data"][i]["total_cash_momey"]);//KGAME余额
                            var text = '<tr class="asset_table_tr"><td>'+date + '</td>';

                             total_new_count += new_count;
                             total_new_incom_moneys += new_incom_moneys;
                             total_new_draw_moneys += new_draw_moneys;
                             total_get_incom_total_moneys += get_incom_total_moneys;
                             total_get_draw_total_moneys += get_draw_total_moneys;
                             total_total_assets_moneys += total_assets_moneys;
                             total_login_count+=login_count;
                            text += '<td>'+ get_select_platform + '</td>';
                            text += '<td>'+ new_count +'</td>';
                            text += '<td>'+ login_count + '</td>';
                            text += '<td>'+ new_incom_moneys + '</td>';
                            text += '<td>'+ new_draw_moneys + '</td>';
                            text += '<td>'+ get_incom_total_moneys.toFixed(2) + '</td>';
                            text += '<td>'+ get_draw_total_moneys.toFixed(2) + '</td>';
                            text += '<td>'+ total_assets_moneys.toFixed(2) + '</td>';
                            text += '</tr>';

                            $("#asset_table").append(text);
                        }
                        var text1;
                        var str='合计';
                        var str2='＼';
                        text1 += '<tr class="add_tpl_view">';
                        text1 += '<td>'+ str + '</td>';
                        text1 += '<td>'+ str2 + '</td>';
                        text1 += '<td>'+ total_new_count + '</td>';
                        text1 += '<td>'+ total_login_count + '</td>';
                        text1 += '<td>'+ total_new_incom_moneys + '</td>';
                        text1 += '<td>'+ total_new_draw_moneys + '</td>';
                        text1 += '<td>'+ total_get_incom_total_moneys.toFixed(2) + '</td>';
                        text1 += '<td>'+ total_get_draw_total_moneys.toFixed(2) + '</td>';
                        text1 += '<td>'+ total_total_assets_moneys.toFixed(2) + '</td>';
                        text1 += '</tr>';
                        $("#asset_table").append(text1);
                    }else{
                        var error_message=data['error_message'];
                        alert(error_message);
                        return false;
                    }
                },
                error : function() {
                }
            });
</script>
</html>