javascript 文件上传进度条 js 上传文件流

var xhr = new XMLHttpRequest();
xhr.open('GET', "http://abc/a.jpg");
xhr.responseType = 'blob';
xhr.onload = function(){
    var content = xhr.response;
    var blob = new Blob([content]);//blob.type=''
    var file2 = new File([blob], 'test.png', {type: 'image/png'});
    let formData = new FormData();
    formData.append('file',file2 );
    //上传接口
}