javascript检查表单数据是否改变

有的时候，需要检查用户是否修改了一个表单中的内容，则可以使用下面的技巧，其中如果修改了表单的内容则返回true，没修改表单的内容则返回false。代码如下：

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.";}};