function check_form() {
  if (document.form.name.value.length < 5) {
    alert('\n    Molim Vas upisite svoje ime i prezime!\n    ');
    document.form.name.focus();
    document.form.name.select();
    return false;
  }

  var text=document.form.email.value;

  if (text.length < 5) {
    alert('\n    Molim Vas upisite E-mail adresu!\n    ');
    document.form.email.focus();
    document.form.email.select();
    return false;
  }
  if(!isEmail(text)) {
      alert("\n  Greska: E-mail adresa je neispravna!\n\n  Molim Vas proverite!");
      document.form.email.focus();
      return (false);
  }

  if (document.form.subject.value.length < 5) {
    alert('\n  Molim Vas upisite temu (subject) poruke!  \n');
    document.form.subject.focus();
    document.form.subject.select();
    return false;
  }

  if (document.form.message.value.length < 5) {
    alert('\n  Molim Vas upisite tekst poruke!  \n');
    document.form.message.focus();
    document.form.message.select();
    return false;
  }

}

function isEmail(entry) {
  var rex= /^.+\@(\[?)[a-zA-Z0-9\-\.]+\.([a-zA-Z]{2,3}|[0-9]{1,5})(\]?)$/;
  return rex.test(entry);
}