Opening and closing a modal dialog using JavaScript

[David Reynolds]

Hi,
Trying to create a page with a responsive sidebar. Just to clarify, I want the menu to appear or disappear at the push of a button.
I've messed around with this for a while, and came up with a modal dialog. However, the button I use to open it doesn't seem to work.
Here's the button code:
   <button onclick = "menuButton()" > Menu</button>
In theory, this should open the modal dialog containing the menu. Here's the associated JavaScript:
  <script>
     const
 menuButton = document.getElementById('menubtn'),
 trueMenu = document.getElementById('true-menu'),
 closeButton = document.getElementById('close-true-menu');

menuButton
 .addEventListener(
   'click',
   () => {
     trueMenu.showModal();
   }
);

closeButton
 .addEventListener(
   'click',
   () => {
     trueMenu.close();
   }
 );
  </script>
I've lost a lot of hair over this one, and any useful hints would be very much appreciated.

[Tim Moores]

Welcome to the Ranch.

This is not a complete, executable code example so it's hard to day what might be going wrong. The first step would be to check the browser's console for any error messages.