判断上传文件的大小

var
  Sys = {};
if
(navigator.userAgent.indexOf(
"MSIE"
)>0) {
    Sys.ie=true
;
}
if
(isFirefox=navigator.userAgent.indexOf(
"Firefox"
)>0){
    Sys.firefox=true
;
}

var
 maxLength = 5*1024*1024;

function
 checkFileChange(obj) {
    var
 filesize = 0;
    if
(Sys.firefox){
        filesize = obj.files[0].fileSize;
    }else
 
if
(Sys.ie){
        var
 filePath = obj.value;
        var
 image=
new
 Image();
        image.dynsrc=filePath;
        filesize=image.fileSize;
    }
    alert(filesize);
}