WebExtension Manifest v3

background.js

// // Called when the user clicks on the browser action.
// chrome.action.onClicked.addListener(function(tab) {
//   // No tabs or host permissions needed!
//   console.log('Turning ' + tab.url + ' red!');
//   // chrome.tabs.executeScript({
//   //   code: 'document.body.style.backgroundColor="red"'
//   // });
// });

chrome.alarms.create({delayInMinutes: 1/60});

chrome.alarms.onAlarm.addListener(function() {
  console.log('hello')
});

// self.addEventListener('install', function(event) {
//   console.log('sw install')
// });

// self.addEventListener('activate', function(event) {
//   console.log('sw activate')
// });

// chrome.action.setBadgeText({ text: `hi` })

const secret = Math.random()

chrome.runtime.onMessage.addListener(
  function(request, sender, sendResponse) {
    console.log(sender.tab ?
                "from a content script:" + sender.tab.url :
                "from the extension");
      sendResponse({ secret });
  });

contentscript.js

console.log('yott')


// code to be injected into inpage
const code = function () {
  function randomFromList(list) {
    return list[Math.floor(list.length * Math.random())]
  }
  function randomColor() {
    return randomFromList(['orange', 'pink', 'lime'])
  }
  function setRandomColor() {
    if (!document.body) return
    document.body.style.backgroundColor = randomColor()
  }

  setTimeout(setRandomColor, 20)
  setInterval(setRandomColor, 10000)
}

// injection (copied from metamask)
injectScript(`(${code})()`)

function injectScript (content) {
  try {
    const container = document.head || document.documentElement
    const scriptTag = document.createElement('script')
    scriptTag.setAttribute('async', false)
    scriptTag.textContent = content
    container.insertBefore(scriptTag, container.children[0])
    container.removeChild(scriptTag)
  } catch (e) {
    console.error('MetaMask script injection failed', e)
  }
}

let latestId = null

function pingBackground() {
  chrome.runtime.sendMessage({greeting: "hello"}, function(response) {
    if (latestId === null) latestId = response.secret
    if (latestId === response.secret) return
    latestId = response.secret
    console.log('sw restarted!')
  });
}

setInterval(pingBackground, 100)

manifest.json

{
  "name": "Page Redder",
  "description": "Make the current page red",
  "version": "2.0",
  "permissions": [
    "activeTab"
  ],
  "background": {
    "service_worker": "background.js"
  },
  "content_scripts": [
    {
      "matches": [
        "file://*/*",
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "contentscript.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "manifest_version": 3
}