XMLHttpRequest 上传进度未正确触发

Tested in chrome and firefox with the same issues. Below is a console log of the event

XMLHttpRequestProgressEvent {totalSize: 764277, position: 764277, total: 764277, loaded: 764277, lengthComputable: true…}
bubbles: false
cancelBubble: false
cancelable: true
clipboardData: undefined
currentTarget: XMLHttpRequestUpload
defaultPrevented: false
eventPhase: 0
lengthComputable: true
loaded: 764277
position: 764277
returnValue: true
srcElement: XMLHttpRequestUpload
target: XMLHttpRequestUpload
timeStamp: 1390945794935
total: 764277
totalSize: 764277
type: "progress"
__proto__: XMLHttpRequestProgressEvent

这是我的源代码 javascript

var formData = new FormData();
formData.append('file', file);

var xhr = new XMLHttpRequest();

xhr.upload.addEventListener("progress", function(e) {
    console.log(e);
}, false);

xhr.onload = function () {
    if (xhr.status === 200) {
        console.log('done');
    } 
    else if (xhr.status == 403) {
        console.log('forbidden');
    }
    else {
        console.log('error');
    }
};

xhr.open("POST", '/upload.php');
xhr.send(formData);