TEXT BOXES ACCEPT ONLY NUMBER USING JAVA SCRIPT?

<script language="javascript" type="text/javascript"

functionisNumericKeyStroke()
{
 varreturnValue = false;
 varkeyCode = (window.event.which) ? window.event.which : window.event.keyCode;

 if ( ((keyCode>= 48) && (keyCode<= 57)) || // All numerics
           (keyCode ==  8) ||     // Backspace
           (keyCode == 13) )     // Carriage Return
         returnValue = true;

 if ( window.event.returnValue )
  window.event.returnValue = returnValue;

 returnreturnValue;
}
</script>