JSFiddle - React, Tailwind, and code Playground

HTML

<select name="dropdown1">
  <option></option>
  <option value="1">Test 1</option>
  <option value="2">Test 2</option>
  <option value="3">Test 3</option>
</select>

<select name="dropdown2">
  <option></option>
  <option value="1">Test 1</option>
  <option value="2">Test 2</option>
  <option value="3">Test 3</option>
</select>

JavaScript

var $dropdown1 = $("select[name='dropdown1']");
var $dropdown2 = $("select[name='dropdown2']");

$dropdown1.change(function() {
    $dropdown2.empty().append($dropdown1.find('option').clone());
    var selectedItem = $(this).val();
    if (selectedItem) {
        $dropdown2.find('option[value="' + selectedItem + '"]').remove();
    }
    
    
    $dropdown2.change(function() {
    $dropdown2.empty().append($dropdown1.find('option').clone());
    var selectedItem = $(this).val();
    if (selectedItem) {
        $dropdown2.find('option[value="' + selectedItem + '"]').remove();
    }
});