检查表单数据是否改变

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 = "You have unsaved changes.";

    }

    // Safari 浏览器

    return "You have unsaved changes.";

  }

};