不跨域的情况下文件下载

const downloadFile = (name, url) => {
    var xhr = new XMLHttpRequest();
        xhr.open('GET', url, true);
        xhr.responseType = 'blob';
        xhr.onload = function (e) {
          if (e.target.readyState === 4 && e.target.status === 200) {
            let blob = this.response;
            // 转换一个blob链接
            let u = window.URL.createObjectURL(new Blob([blob]));
            let a = document.createElement('a');
            a.download = name;
            a.href = u;
            a.style.display = 'none';
            document.body.appendChild(a);
            a.click();
            a.remove();
          }
        };
        xhr.send();
 }