Persistent Service Worker in Chrome Extension

This is caused by these problems in ManifestV3:

crbug.com/1024211, the worker doesn’t wake up for webRequest events.
The workarounds are listed below.
crbug.com/1271154, the worker is randomly broken after an update.
Mostly fixed in Chrome 101.
Per the service worker (SW) specification, it can’t be persistent and the browser must forcibly terminate all of SW connections such as network requests or ports after some time, which in Chrome is 5 minutes. Chromium team currently considers this behavior intentional and good for extensions, because the team never investigated real world situations where this SW behavior is bad in case an extension has to observe frequent events:
- chrome.tabs.onUpdated/onActivated,
- chrome.webNavigation if not scoped to a rare url,
- chrome.webRequest if not scoped to a rare url or type,
- chrome.runtime.onMessage/onConnect for messages from content script in all tabs.
Such events are generated in response to user actions, so there are natural pauses for a few minutes, during which the SW is terminated. Then it starts again for a new event, which takes at least 50ms to create the process plus the time to load and compile your code, ~50ms on the average, i.e. it’s ~100 times heavier than ~1ms needed to call a simple JS event listener. For an active online user it may restart hundreds of times a day thus wearing down CPU/disk/battery and often introducing a frequent perceivable lag of the extension’s reaction.

Workarounds

For webRequest not waking up

Additionally subscribe to an API like chrome.webNavigation as shown in the other answer(s).

This applies to extensions that observe infrequent events, e.g. you specified urls filter for webRequest/webNavigation for just one rarely visited site. Such extensions can be reworked to avoid the need for a persistent background script so it will start only a few times a day, which will be good for memory footprint while not stressing CPU too much. You would save/load the variables/state in each listener via chrome.storage.session (temporary, 1MB max), or chrome.storage.local, or even IndexedDB that’s much faster for big/complex data.

But if you MUST observe frequent events (listed in the beginning of this answer), you’ll have to prolong the background script’s lifetime artificially using the following workarounds.

“Persistent” service worker while a connectable tab is present

In case you don’t use ports with a content script that runs in all tabs (shown in another workaround below), here’s an example of opening a runtime port from any tab’s content script or from another page of the extension like the popup page and reconnecting it before 5 minutes elapse.

Downsides:

The need for an open web page tab or an open extension tab/popup.
Broad host permissions (like <all_urls> or *://*/*) for content scripts which puts most extensions into the slow review queue in the web store.

Warning! Also implement the workaround for sendMessage (below) if you use sendMessage.

Warning! You don’t need this if you already use the workaround for chrome.runtime.connect (below) with a content script that runs in all tabs.

manifest.json, the relevant part:

  "permissions": ["scripting"],
  "host_permissions": ["<all_urls>"],
  "background": {"service_worker": "bg.js"}

background service worker bg.js:

let lifeline;

keepAlive();

chrome.runtime.onConnect.addListener(port => {
  if (port.name === 'keepAlive') {
    lifeline = port;
    setTimeout(keepAliveForced, 295e3); // 5 minutes minus 5 seconds
    port.onDisconnect.addListener(keepAliveForced);
  }
});

function keepAliveForced() {
  lifeline?.disconnect();
  lifeline = null;
  keepAlive();
}

async function keepAlive() {
  if (lifeline) return;
  for (const tab of await chrome.tabs.query({ url: '*://*/*' })) {
    try {
      await chrome.scripting.executeScript({
        target: { tabId: tab.id },
        function: () => chrome.runtime.connect({ name: 'keepAlive' }),
        // `function` will become `func` in Chrome 93+
      });
      chrome.tabs.onUpdated.removeListener(retryOnTabUpdate);
      return;
    } catch (e) {}
  }
  chrome.tabs.onUpdated.addListener(retryOnTabUpdate);
}

async function retryOnTabUpdate(tabId, info, tab) {
  if (info.url && /^(file|https?):/.test(info.url)) {
    keepAlive();
  }
}

If you also use sendMessage

Always call sendResponse() in your chrome.runtime.onMessage listener even if you don’t need the response. This is a bug in MV3. Also, make sure you do it in less than 5 minutes time, otherwise call sendResponse immediately and send a new message back via chrome.tabs.sendMessage (to the tab) or chrome.runtime.sendMessage (to the popup) after the work is done.

If you already use ports e.g. chrome.runtime.connect

Reconnect each port before 5 minutes elapse.

background script example:

chrome.runtime.onConnect.addListener(port => {
  if (port.name !== 'foo') return;
  port.onMessage.addListener(onMessage);
  port.onDisconnect.addListener(deleteTimer);
  port._timer = setTimeout(forceReconnect, 250e3, port);
});
function onMessage(msg, port) {
  console.log('received', msg, 'from', port.sender);
}
function forceReconnect(port) {
  deleteTimer(port);
  port.disconnect();
}
function deleteTimer(port) {
  if (port._timer) {
    clearTimeout(port._timer);
    delete port._timer;
  }
}

client script example e.g. a content script:

let port;
function connect() {
  port = chrome.runtime.connect({name: 'foo'});
  port.onDisconnect.addListener(connect);
  port.onMessage.addListener(msg => {
    console.log('received', msg, 'from bg');
  });
}
connect();

“Forever”, via a dedicated tab, while the tab is open

Open a new tab with an extension page inside e.g. chrome.tabs.create({url: 'bg.html'}).

It’ll have the same abilities as the persistent background page of ManifestV2 but a) it’s visible and b) not accessible via chrome.extension.getBackgroundPage (which can be replaced with chrome.extension.getViews).

Downsides:

consumes more memory,
wastes space in the tab strip,
distracts the user,
when multiple extensions open such a tab, the downsides snowball and become a real PITA.

You can make it a little more bearable for your users by adding info/logs/charts/dashboard to the page and also add a beforeunload listener to prevent the tab from being accidentally closed.

Future of ManifestV3

Let’s hope Chromium will provide an API to control this behavior without the need to resort to such dirty hacks and pathetic workarounds. Meanwhile describe your use case in crbug.com/1152255 if it isn’t already described there to help Chromium team become aware of the established fact that many extensions may need a persistent background script for an arbitrary duration of time and that at least one such extension may be installed by the majority of extension users.