js 文件下载进度监控

    var xhr = new XMLHttpRequest();
    xhr.open('GET', '文件地址.mp4');
    xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xhr.responseType = "blob";
    xhr.onprogress = function (event) {
        if (event.lengthComputable) {
            console.log(event.loaded);
            console.log(event.total);12         }
    };
    xhr.onload = function (oEvent) {
        console.log(oEvent);
        console.log(xhr.status);
        console.log(xhr.response);
        if (xhr.readyState === 4 && xhr.status === 200) {
            // var name = xhr.getResponseHeader("Content-disposition");
            // var filename = name.substring(20,name.length);
            var blob = new Blob([xhr.response], {type: 'video/mp4'});
            var csvUrl = URL.createObjectURL(blob);
            var link = document.createElement('a');
            link.href = csvUrl;
            link.download = 'abababababba.mp4';
            link.click();          
        }
    }
    xhr.send();