<select id="mySelect">
<option id="option1">選項1</option>
<option id="option2">選項2</option>
<option id="option3">選項3</option>
</select>

javascript
function getOptionId() {
var selectElement = document.getElementById("mySelect");
var selectedOption = selectElement.options[selectElement.selectedIndex];
var optionId = selectedOption.id;
// 使用Ajax發送請求，并傳遞optionId作為參數
// ...
}