js发送post请求，实现下载文件

由于业务需求要下载文件的功能：
  <!DOCTYPE html>
        <html>
        <head>
            <meta charset="utf-8">
            <meta name="renderer" content="webkit|ie-comp|ie-stand">
            <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
            <meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no"/>
            <meta http-equiv="Cache-Control" content="no-siteapp"/>
            </head>
            <body>
            <input type="button" id="clickme" value="clickme" />
            </body>
             <script type="text/javascript">
             function postExcelFile(params, url) { //params是post请求需要的参数，url是请求url地址
                var form = document.createElement("form");
                form.style.display = 'none';
                form.action = url;
                form.method = "post";
                document.body.appendChild(form);

                for(var key in params){
                  var input = document.createElement("input");
                  input.type = "hidden";
                  input.name = key;
                  input.value = params[key];
                  form.appendChild(input);
                }
                
                form.submit();
                form.remove();
              }
              //点击导出按钮导出excel表格
              clickme.onclick = function() {
                var params = {};
                //params.queryDateEnd='20180709';
                //params.queryDate='20180709';
                //params.productId=0;
                // params.chnMerchant='咪咕视讯,咪咕+,内部导流';
                //params.chnAttr='咪咕视讯自有渠道,咪咕互娱';
//params.chnID='101700010000009,308500040040028,101800000030119,10290001916,101400030060133';
                //postExcelFile(params, "http://localhost:8082/kpi/chnOperate/export");
                
                params.queryDate='2018-08-16';
                params.productId=0;
                params.channel1Id='12924,12925,12926';
                params.channel2Id='332584,12927,333950,314216';
                //params.channel3Id='332585,12938,333951';
                //params.channel4Id='335273,332081,336699';
                //params.chnID='201600010000758,202400000000006';
                  postExcelFile(params, "http://wxs.ngrok.xiaomiqiu.cn/kpi/chnOperate/realTime/daily/list/export");
              }

             </script>
            </html>