＜a＞标签，跨域download属性不生效问题，100%好用

<a click="downloadFile(fileUrl,fileName)">下载文件</ a>

downloadFile(url, fileName) {
    var x = new XMLHttpRequest();
    x.open("GET", url, true);
    x.responseType = 'blob';
    x.onload=function(e) {
        var url = window.URL.createObjectURL(x.response)
        var a = document.createElement('a');
        a.href = url
        a.download = fileName;
        a.click()
    }
    x.send();
},