JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form>
<select id="mySelect">
  <option selected>Select colour</option>
  <option value="Orange">Orange</option>
  <option value="Apple">Apple</option>
  <option value="Lemon">Lemon</option>
</select>
  <button id="submit-button" type="submit">Click</button>
</form>

JavaScript

// Executed when DOM is loaded
$(document).ready(function() {
   // Executed when select is changed
    $("select").on('change',function() {
        var x = this.selectedIndex;

        if (x == "") {
           $("#submit-button").hide();
        } else {
           $("#submit-button").show();
        }
    });
    
    // It must not be visible at first time
    $("#submit-button").css("display","none");
});