uploader 上传文件，当在上传过程中断开网络，异常无法处理

uploader 上传文件，当在上传过程中断开网络，异常无法处理。  
我在调试时候打印出，文件已经上传的大小，与文件总大小。当文件上传到一定比率，突然断开网络，控制台打印出  ‘Uncaught SyntaxError: Unexpected token }’这样的语句！？？？？关键是这个异常我不知道怎样捕获？下面是我监听 uploader的 onStateChanged事件的函数：  

function onStateChanged( upload, status ) {
try
{
var percent = parseInt((upload.uploadedSize/upload.totalSize)*100);
//var percent = 20;
console.log(upload.uploadedSize + "," + upload.totalSize);
if (!isNaN(percent)){
if (10<percent<100){
progress.style.width = percent + "%" ;
}else if (percent == 100){
//width: 50% auto;
progress.style.width = percent + "% auto" ;
}
progresstxt.innerText = percent+"%";
//alert(filesSizeInf[0].name + "," +filesSizeInf[0].size);
if (finishFileCount<filesSizeInf.length && upload.uploadedSize >= filesSizeInf[finishFileCount].size){
finishinfo.innerText = "已经上传" + (++finishFileCount)+"/" +files.length+"张";
//alert("已经上传" + finishFileCount+"张,共" +files.length+"张,文件名称");
}
}
//alert('完成比率：' + percent);
if ( upload.state == 4) {
//alert( "Upload success: " + upload.getFileName());
if (status == 200){
files=[];
document.getElementById("imgList").innerHTML = "";
}
}
}catch (e){
alert("状态错误" + e.message);
}

}