JSFiddle - React, Tailwind, and code Playground

HTML

<form action="somepage.asp" method="get"> 

<select id="num_rooms" name="Rooms">
    <option value="1">1 Room</option>
    <option value="2">2 Rooms</option>
    <option value="3">3 Rooms</option>
    <option value="4">4 Rooms</option>
</select>

<select id="solutionId" name="oldGuests">
    <option value="1">1 Guest</option>
    <option value="2" selected="">2 Guests</option>
    <option value="3">3 Guests</option>
   <option value="4">4 Guests</option>
</select>
<select id="solutionId" name="newGuests">
    <option value="1">1 Guest</option>
    <option value="2" selected="">2 Guests</option>
    <option value="3">3 Guests</option>
   <option value="4">4 Guests</option>
   <option value="5">5 Guest</option>
    <option value="6">6 Guests</option>
    <option value="7">7 Guests</option>
   <option value="8">8 Guests</option>
</select>

<input type="submit">
</form>

JavaScript

$("#num_rooms").change(function(){
  if($("#num_rooms").val()==1){
  	alert("hi");
  }
})