javascript cloneNode() doesn't work properly

I have in an html page a select element with an id="a" (for example). I have a function called f(). when I write

$("#a").on("change",f);

it works, meaning every time I change the selected value in the drop down list the function f() is called.

I want to clone this select in another place in the page. I have this code:

var oldSelect=$("#a")
var newSelect=oldSelect[0].cloneNode(true);
newSelect.id="b";
$("#b").on("change",f);

and when I change the selected value in the new dropdown list, the function f() isn't called.

I tried debugging it using the chrome's devTools and it apears that $("#a") is kind of an array length 1 that in the first place has the select itself. But $("#b") doesn't have the "0" property containing the select itself.

Does anyone know why does it happen? how can I clone a select element with all its options and callbacks?

Although you cloned the existing #a, you haven't inserted it into the document yet in the code you've shown, so $("#b") will not give you any elements in return. Either insert it before selecting it with $, eg:

$(container).append(newSelect);
$("#b").on("change",f);

where container is the element you want to append the new <select> to.

Or add the listener directly to the element, instead of selecting it again:

var newSelect=oldSelect.clone(true);
newSelect
  .prop('id', 'b')
  .on("change",f)
  .appendTo(container);

(Note that in the above, newSelect is a jQuery collection, not an HTMLSelectElement.)

const f = () => console.log('change');

var oldSelect = $("#a");
oldSelect.on("change",f);

var newSelect = oldSelect.clone(true);
newSelect
  .prop('id', 'b')
  .on("change", f)
  .appendTo('#container');

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="container">
  <select id="a">
    <option>Option A</option>
    <option>Option B</option>
  </select>
</div>