Getting validation for entering only numeric values using javaScript

<html>
<head>
<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  value : <input type='text' onkeypress='validate(event)' />
</body>
</html>