function numbersonly(e) {
  
  try
  {
    var unicode=e.charCode? e.charCode : e.keyCode;
    
    if (unicode!=8)
    { //if the key isn't the backspace key (which we should allow)
      if (unicode<48||unicode>57)
      {
        alarm("Zadajte číslo prosím");
        return false; //if not a number return false //disable key press
      }
    }
    return true;
  }
  catch(err)
  {
    var txt="Error description numbersonly: " + err.description + "\n\n";
    txt+="Click OK to continue.\n\n";
    alert(txt);
  }
}