IE不会正确生成XMLHttpRequest.upload.onprogress事件

Question

我并行发送4个POST请求。 Chrome和Firefox等普通浏览器均匀生成上传进程事件。 但IE（在版本10和11上测试）仅在请求完成或中止或上载一半时生成事件。我的代码如下所示：

function XHRUpload(/* ... */) {
    //...
    this.request = new XMLHttpRequest();
    this.request.onreadystatechange = function() {};
    this.request.upload.onprogress = function(e) {
        console.log(e.loaded, e.total);
    };
    this.request.onerror = function(e, msg) {
        //...
    };
    this.request.ontimeout = function(e, msg) {
        //...
    };
    this.request.open('POST', this.url, true);
    this.request.setRequestHeader('Content-Type', 'text/plain;charset=utf-8');
}

XHRUpload.prototype.upload = function() {
    this.request.send(this.options.data);
};

XHRUpload.prototype.abort = function() {
    this.request.abort();
};