JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://raw.githubusercontent.com/HubSpot/offline/v0.7.11/offline.min.js"></script>
<p> Hello there ! this is my first Offline test </p>

JavaScript

Offline.options = {checkOnLoad: true, checks: {image: {url: 'http://www.vitaminedz.com/photos/49/02-49565-front-de-mer-a-oran.jpg'}, active: 'image'}}
  function up() {
      
     alert('up'); 
  }

  function down() {
      
     alert('down'); 
  }
    console.log(Offline)

    Offline.on('up', up());
    Offline.on('down',down());