//使用表单下载

 function commDownload(url, method, params) {

     let formStr = `<form action="${url}" method="${method}" >`;

     for(let [key, value] of Object.entries(params)) {

         formStr += `<input type="text" name="${key}" value="${value}" />`;

     }

     formStr += "</form>";

     $(formStr).appendTo("body").submit().remove();

 }

 //使用url跳转下载

 function commDownload2(url, params) {

     url += "?";

     for(let key in params) {

         url += key + "=" + params[key] + "&";

     }

     url = url.substr(0, url.length - 1);

     window.open(url);

 }

 //使用a标签下载--推荐使用

 function commDownload3(url, params) {

     url += "?";

     for(let key in params) {

         url += key + "=" + params[key] + "&";

     }

     url = url.substr(0, url.length - 1);

     $("<a href=" + url + " />")[0].click();

 }