i want to show a text box in a web apllication

i hav used following code

<script type ="text/jscript" language ="javascript" >
function validatedata()
{
if(window.document.form1.txtQuan.Value=='')
{
alert("Please Enter Quantity");
document.form1.txtQuan.Focus();
return false;
}
}
</script>

in aspx page

& this
btnDelete.Attributes.Add("onclick", "return validatedata();");
on .cs

but its not working

plz help me out

thnx
shikha