errorgif = new Image(); 
errorgif.src = "http://www.1a-malerwerkzeuge.com/out/malerbedarf/src/bg/sirene.gif";
spacer = new Image();
spacer.src = "http://www.1a-malerwerkzeuge.com/out/malerbedarf/src/bg/spacer.gif";

function validate_form() {
  validity = true; // assume valid
  if (!check_empty(document.callback.c_name.value))
        { validity = false; document.name_err.src = errorgif.src;
          
        } else {
          document.name_err.src = spacer.src;
 }
  if (!check_telefon(document.callback.c_telefon.value))
        { validity = false; document.telefon_err.src = errorgif.src;
          
        } else {
          document.telefon_err.src = spacer.src;
 }
  if (validity);
  return validity;
}

function check_empty(text) {
  return (text.length > 0); // wenn leer, error
}

function check_telefon(number) {
  if ((number == "")
    || (number.match(/[^\d\/+-]+/)))
      return false;
  return true;
}

function setLink(link){
    document.getElementById('linker').href= link
}