javascript檢查表單數據是否改變

有的時候，需要檢查用戶是否修改了一個表單中的內容，則可以使用下面的技巧，其中如果修改了表單的內容則返回true，沒修改表單的內容則返回false。代碼如下：

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"])) {
		if (e) {
			e.returnValue = "You have unsaved changes.";
		}
		return "You have unsaved changes.";
	}
};