Passing a value from a service worker to HTML

I am trying to improve a progressive web app that I made fairly recently. To save a little time when developing and to reduce the risk of an error I would like to display the version number automatically instead of manually copying it into HTML.

The version number is defined as the cache name in the service worker:

const cacheName = '1.6.2';

The service worker is registered by register.js which is called in the head of each HTML page.

<script src="register.js" defer></script>

Then in a script at the end of the body I have:

document.getElementById('versionNo').innerHTML = cacheName;

And in the HTML:

<span id="version">Version: <span id="versionNo"></span></span>

However this leaves the version number blank and the javascript console reports “jquery.js:2 Uncaught ReferenceError: cacheName is not defined”. Is there an error in my thinking or is this just not possible?