medium background script v1

background.js

chrome.runtime.onInstalled.addListener(() => {
  console.log('onInstalled...');
  // create alarm after extension is installed / upgraded
  chrome.alarms.create('refresh', { periodInMinutes: 3 });
});

chrome.alarms.onAlarm.addListener((alarm) => {
  console.log(alarm.name); // refresh
  helloWorld();
});

function helloWorld() {
  console.log("Hello, world!");
}

@atomauro chrome is available for Chrome and Firefox, where are you getting this error? If it is eslint you should ignore it. https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/onInstalled