var oneShot = function (that) {
  var elements = that.elements;
  var i;
  for (i = 0; i < elements.length; i += 1) {
    if (elements[i].type === 'submit') { elements[i].disabled = true; }
  }
};


var agree = function (that) {
  if (!document.forms[0].agreement.checked) {
    alert('規約に同意の場合にはチェックしてください。');
    return false;
  } else {
    oneShot(that);
    return true;
  }
};