Validating textboxes without postback

function validate()
{
 var txt1=document.getElementById("<%=txtBox1.ClientID%>");
 if(txt1.value=="")
{
return false;

}
 }

call this function using Button OnClientClick="return validate();"

function()
{
if (document.getElementById('txt_toId').value == '') {
     alert('Please Enter To Code!');
      document.getElementById('txt_toId').focus();
       return false;
                }
                else {
                    return true;
                }
}

<script language="javascript" type="text/javascript">
        function ValidateSaveRegion() {

            var Date = document.getElementById('cntPlcHolder_txtDate');

if (Date.value.match(/^\s+$/) || Date.value == "") {

                alert('Enter Date');
                Date.focus();
                return false;
            }