Here is one example :
javascript code :
function test() {
var x = document.getElementById('fname').value;
var y = document.getElementById('pwd').value;
alert(x.length + ' ' + y.length);
if ((x.length > 8) && (y.length > 8)) {
document.getElementById('form1').submit();
return true;
}
else {
alert("user name should contain 8 characters");
return false;
}
}
Html code :
<form id="form1" runat="server" method="get" action="test.htm">
Enter name
<input type="text" id="fname" />
enter password<input type="password" id="pwd" />
<input type="submit" value="login" onclick="return test();" />
</form>
good luck.