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：

复制代码 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.";

}

};