How do you manage errors in your service workers?

1 What are service workers and why do they fail?

Service workers are JavaScript files that run in the background of your web app and intercept network requests, cache assets, and perform other tasks. They are registered and activated by your main app, but they have their own scope and lifecycle. Service workers can fail due to syntax errors or bugs in the code, network errors or timeouts when fetching the script or its dependencies, mismatched or outdated versions of the service worker or the cached assets, or user actions or browser settings that disable or delete the service worker or the cache.

2 How to debug service workers in development?

In order to manage errors in your service workers, debugging them in development is a must. Chrome DevTools Application panel can be used to inspect the registration, activation, and events of the service worker, as well as the cache storage and indexedDB data. Additionally, the Network panel monitors network requests and responses handled by the service worker, and you can filter them by type, status, or initiator. The Console panel logs messages, errors, and warnings from the service worker while the Sources panel allows you to set breakpoints and step through the service worker code. Moreover, you can use Chrome DevTools' Update on reload option to force the service worker to update every time you reload the page; Skip waiting option to activate the new service worker immediately; and Offline option to simulate offline mode and test how your service worker handles network failures.

3 How to handle errors in service worker code?

Even if you debug your service worker code thoroughly, you may still encounter errors at runtime that can affect your app's functionality or user experience. To handle these errors, try-catch blocks should be used to wrap any code that may throw an error, such as fetching resources, accessing caches, or parsing data. Additionally, event listeners should be used to handle specific errors that may occur in the service worker lifecycle and event.waitUntil() should be used to extend the event lifetime until the error is resolved or rejected. To check for updates to the service worker script periodically, self.registration.update() should be used and self.skipWaiting() and clients.claim() should be used to activate the new service worker and take control of the clients as soon as possible. If the service worker becomes corrupted or obsolete, self.registration.unregister() should be used to unregister it and caches.delete() should be used to delete any caches that may contain stale or invalid assets.

4 How to handle errors in cached assets?

One of the main benefits of service workers is that they can cache assets and serve them from the cache when the network is unavailable or slow. However, this also means that you need to handle errors in cached assets, such as missing or outdated assets that may cause your app to break or display incorrectly, corrupted or invalid assets that may cause your app to crash or behave unexpectedly, and large or excessive assets that may consume too much storage space or bandwidth. To handle these errors, you can use cache.add() or cache.addAll() to cache assets during the service worker installation and use cache.put() to update assets during the service worker activation or fetch events. You can also use cache.match() or cache.matchAll() to retrieve assets from the cache during the service worker fetch event and use cache.delete() to remove assets from the cache when they are no longer needed. Additionally, you can use cache.keys() to list all the assets in a cache and use caches.match() or caches.matchAll() to search across all the caches in the cache storage for implementing various strategies such as limiting the number or size of cached assets, using expiration or versioning strategies, implementing a cache fallback or network-first strategy, and so on.

5 How to handle errors in user feedback?

When managing errors in your service workers, it's important to provide user feedback and guidance. You can use self.clients.matchAll() to get a list of all the clients controlled by the service worker and client.postMessage() to send messages or data to the clients, which can be used to communicate with the main app about service worker status, errors, or updates. Additionally, you can leverage the Notification API to display notifications to the user about service worker events, errors, or updates. These notifications should include notification actions that allow the user to interact with them, such as refreshing the page, clearing the cache, or updating the service worker. Furthermore, you can use ServiceWorkerRegistration.showUpdateUI() to show a default update UI when the service worker has an update and prompt the user to reload the page or accept the update. Finally, you can use ServiceWorkerContainer.register() options to configure the service worker registration and customize its behavior and user experience by specifying its scope, update frequency, or user interaction mode.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?