validate time field

I have fields on my web page where users need to enter time in hours and minutes in hh:mm format
e.g <input name="START_MON" type="text" id="START_MON" value="<%= DoDateTime((Recordset1.Fields.Item("START_MON").Value), 4, 1033) %>"  size="10" maxlength="5">.
Is there a way of inserting a validation to showing an alert if the time is entered in the wrong format

 Thank you
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you can use regular expressions.

and use this as the regular expression that you pass to it:

and then call this function
// this field checks retular expressions and takes the following
// RegExp = Regular Expression to check against
// checkField = the field being checked
// checkValue = the value validing the RegExp against
// ErrorMsg = error to display
function regularExpCheck(RegExp, checkField, checkValue, ErrorMsg){
      if (RegExp.test(checkValue)){            
            return (true);
      //not valid, give error, set focus and give error
      return (false);
Presuming you have a submit button to validate this form, add this function and then add an onClick event with the following onClick(return ValidateTime(this)). If the time does doesn't match a hh:mm format (24hr format as well), then it will return false, stop the p[age submission and trigger one of the alerts.


function ValidateTime(Input)
	var regex = /^([0-9]{1,2})[:. ]([0-9]{1,2})$/;
	var matches = Input.value.match(regex);
	if ( matches != null )
		if ( matches[1] < 0 || matches[1] > 24 )
			alert( "Please enter a valid 24hr time\n\nThe hour must be between 00 and 24" );
			return false;
		if ( matches[2] < 0 || matches[2] > 59 )
			alert( "Please enter a valid 24hr time\n\nThe minute must be between 00 and 59" );
			return false;
		alert( "Please enter a valid 24hr time format (hh:mm)" );
		return false;
	return true;

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I didn't include 24:00, as it's usually just shown as 0:00.
Rarely does anyone refer to it as 24:00, but it's easy to add in.
<script type="text/javascript">
function val12hr(){
  var ret = document.getElementById('START_MON').value.match(/^(0?[0-9]|^1[0-2])\:[0-5][0-9]$/);
  if(ret) return true;
  else {alert('Invalid 12 hour time'); return false; }
function val24hr(){
  var ret = document.getElementById('START_MON').value.match(/^([0-1]?[0-9]|^2[0-3])\:[0-5][0-9]$/);
  if(ret) return true;
  else { alert('Invalid 24 hour time'); return false; }
<input name="START_MON" type="text" id="START_MON" value="<%= DoDateTime((Recordset1.Fields.Item("START_MON").Value), 4, 1033) %>"  size="10" maxlength="5" onBlur="val12hr()"></input>

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CamnocAuthor Commented:
Thank you
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