js检测离开或刷新页面时表单数据是否更改的方法

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？";  }};