简单来说
1. button可以携带value值，并且在点击button时候，form提交会带上button的value
<button name="foo" value="bar" type="submit">Submit</button>
2. button带值可以有多个
<form action="/test-form" method="post"> <button name="_action" value="delete" type="submit">Delete</button> <button name="_action" value="disable" type="submit">Disable</button> </form>
3. 直接 new FormdData 不会携带button的value
const formdata = new FormData(form);
4. 使用 submitter 参数，可以指定提交某个button的value
form.addEventListener("submit", function (event) {
event.preventDefault();
const formdata = new FormData(form, event.submitter);
});