Need help to get file size while uploading

[eluser]nandish[/eluser]
I try to avoid uploading images according to file size but the thing is am not able to get file size with the help of javascript



function getFilesize(){
var size = document.images['uimgs'].fileSize;
return size;
}
function validate(){
alert(getFilesize();
}
If i run this script its return undefined in both IE AND FIREFOX


Thanks in Advance