How To Validict Textbox Through Javascript

Firstly make the function in Javascript to validate Textbox:-

/*We can write this code under <script src="JScript.js" type="text/javascript">

function check_blank(fldid, msgid) {

    var fld = document.getElementById(fldid);

    if (fld.value.length == 0 || fld.value.charAt(0) == " ") {

        document.getElementById(msgid).innerHTML = "Require field has not been filled";

        return false;

    }

    document.getElementById(msgid).innerHTML = "&nbsp";

    return true;

}

 </script>

Call this function on Aspx page:-

Like if u want to validate Textbox  then simple call upper code on aspx page like as:-

  <asp:TextBox ID="Tname" onblur="return check_blank(this.getAttribute('id'),'fname')" runat="server" Height="32px" Width="285px"></asp:TextBox>

<td><span id="fname" style=" font-size:x-small;color:red;"></span></td>