Validation for enter numeric value only using scripting

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
 <head>
  <title> New Document </title>
  <meta name="Generator" content="EditPlus">
  <meta name="Author" content="">
  <meta name="Keywords" content="">
  <meta name="Description" content="">
  <script>
function validate(evt) {

  var theEvent = evt || window.event;
  var key = theEvent.keyCode || theEvent.which;
  key = String.fromCharCode( key );
  var regex = /[0-9]|\./;
  if( !regex.test(key) ) {
 alert("Enter numeric only...");
    theEvent.returnValue = false;
    if(theEvent.preventDefault) theEvent.preventDefault();
  }
  }
</script>
 </head>

 <body>
  Enter Your ID <input type="text" value="" onkeypress='validate(event)'/>
 </body>
</html>