JavaScript 检测表单数据变更并拦截页面离开

function formIsDirty(form) {
  for (var i = 0; i < form.elements.length; i++) {
    var element = form.elements[i];
    var type = element.type;
    if (type == "checkbox" || type == "radio") {
      if (element.checked != element.defaultChecked) {
        return true;
      }
    }
    else if (type == "hidden" || type == "password" || type == "text" || type == "textarea") {
      if (element.value != element.defaultValue) {
        return true;
      }
    }
    else if (type == "select-one" || type == "select-multiple") {
      for (var j = 0; j < element.options.length; j++) {
        if (element.options[j].selected != element.options[j].defaultSelected) {
          return true;
        }
      }
    }
  }
  return false;
}
window.onbeforeunload = function (e) {
  e = e || window.event;
  if (formIsDirty(document.forms["someForm"])) {
    // IE 和 Firefox
    if (e) {
      e.returnValue = "对不起，页面数据已做修改，尚未保存，确定要刷新或离开本页面？";
    }
    // Safari浏览器
    return "对不起，页面数据已做修改，尚未保存，确定要刷新或离开本页面？";
  }
};