更改前获取选择（下拉）的值

将 焦点 事件与 更改 事件结合起来即可实现所需的目标：

(function () {    var previous;    $("select").on('focus', function () {        // Store the current value on focus and on change        previous = this.value;    }).change(function() {        // Do something with the previous value after the change        alert(previous);        // Make sure the previous value is updated        previous = this.value;    });})();