上传文件进度显示

使用h5+上传文件,监听上传进度的时候,永远就是 0% 然后100%
实际文件还远远没有上传完成.

task.addData("client", "HelloH5+");  
                task.addData("uid", getUid());  
                task.addEventListener("statechanged", onStateChanged, true);  
                for(var i = 0; i < files.length; i++) {  
                    var f = files[i];  
                    task.addFile(f.path, {  
                        key: f.name  
                    });  
                }  
                task.start();

function onStateChanged(upload, status) {  
                console.log(JSON.stringify(upload));  
                console.log(JSON.stringify(status));  

                if(upload.state == 3) {  
                    var percent = Math.ceil(upload.uploadedSize/upload.totalSize*100);  
                     outLine("Uploading: " + percent + "%");  

                }  
        }