thanks guys
I have done something like that
.js file
function chkBlank(objId, lblText)
{
if(objId.value == "")
{
alert("Please enter " + lblText);
objId.focus();
return false;
}
else
{
return true;
}
}
.aspx file
<script type="text/javascript" src="../JS/Validation.js"></script>
<script type="text/javascript" language="javascript">
function Validate()
{
if(chkBlank(document.getElementById('txtuserid'),document.getElementById('lblUserId').innerText) == false){return false;}
if(chkBlank(document.getElementById('txtpwd'),document.getElementById('lblPwd').innerText) == false){return false;}
}
.aspx.vb
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
txtuserid.Focus()
imgblogin.Attributes.Add("onclick", "javascript:return Validate();")
End Sub