function is_number(input) {
  return !isNaN(trim(input));
}

function is_empty(input) {
  return trim(input) == '';
}

function trim(input) {
  return input.replace(/^\s+|\s+$/g,"");
}

function get(id) {
  return trim(document.getElementById(id).value);
}

function required(id, message) {
  var element = document.getElementById(id);
  if(is_empty(element.value)) {
    alert(message);
    element.focus();
    return false;
  }
  return true;
}

function rexmatch(id, rex, message) {
  var element = document.getElementById(id);
  var regex = new RegExp(rex, "i");
  if(!regex.test(trim(element.value))) {
    alert(message);
    element.focus();
    return false;
  }
  return true;
}

function email(id, message) {
  var element = document.getElementById(id);
  var regex = /^.+@.+\.[a-z]{2,6}$/i;
  if(!regex.test(trim(element.value))) {
    alert(message);
    element.focus();
    return false;
  }
  return true;
}

function strlen(id, limit, message) {
  var element = document.getElementById(id);
  if(element.value.length < limit) {
    alert(message);
    element.focus();
    return false;
  }
  return true;
}