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    Use a no-op Service Worker in Development

    Alex Jover MoralesAlex Jover Morales

    Having to manually unregister the Service Worker and clean the cache after you finish testing a Service Worker is ok, but at some point you’d rather automate it.

    ServiceWorkerRegistration.unregister() can only be used within a registration and it doesn’t clean the cache, making it useless for the case.

    However, using a no-operation (no-op) service worker will override the already registered one and remove the cache, leaving it in a clean slate.

    The lesson shows how to automated this by creating a no-op Service Worker to use on development.



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    Instructor: 00:00 First, we need to create a service worker for development. Let's call this service-worker-dev.js. This service worker has to do nothing else than just overwriting the production service worker. For that, we can write self.addEventListener. On the install event, we need to call a function that calls self.skipWaiting. This will force the service worker to be activated.

    00:35 We could have other apps running under the same pair of host and port, so it would be nice if we can refresh them, as well. For that, let's add another event listener for the activate event. We can access other tabs and windows this service worker is running on by typing client, which we have to filter using matchAll of type window.

    01:05 This returns a promise with the client as the payload. Then we need to iterate over those clients. Let's use that for client of clients. To refresh them, we can use the client navigate method, passing the client URL as a parameter.

    01:28 We still need to use this service worker. The way you may think we can do that is by registering the dev service worker on development and the other on production. Let's try that out. In the main file, we could add another condition when it's not production. Then you see it here, should service-worker-dev. Let's copy/paste this down here. Instead, we're going to register the dev service worker.

    02:16 Now let's run the app in production. Let's type npm run build and http-server-c-1. Now let's reload the page and make it bigger. You can see here the service worker is registered, and this is the use file service worker we use in production.

    02:46 If we stop this and we run npm run dev, we reload, and supposedly the dev service worker should have been installed. Let's reload again and let's go to the application tab. We see that the production service worker is still registered. We see this is the production service worker. The question is why is this happening.

    03:14 If you think carefully, this file, the main.js file, is cached by the service worker. The browser is serving this cache my main.js file, which at the point of caching, production was true. The service worker that is going to be registered is always this one. Then we can unload one service worker or another on the registration level.

    03:38 Instead, what we can do is only register one service worker and stop it, depending on the environment. For that, let's remove these conditions and also these else. Let's keep the condition for when the service worker exists in Navigator, and then we unregister this service worker.

    04:02 Then let's go to the package-json. Here, I'm going to add a pre-dev script, which will be run before the dev script because of the pre-prefix. This script will copy the service-worker-dev.js file to service-worker.js. For development, the service worker file will be overwritten.

    04:30 If you want this cp command to work in all platforms, you can install npm install cp. That will install a cross-platform cp command.

    04:42 Finally, let's run npm run dev. If we check this service worker, this one is the development service worker. Let's then go here and reload. You can see that the development service worker has overwritten the production one.

    05:00 If we go to the application and refresh the cache, you'll see there is no cache. This is perfect for development, because even if there were some service worker caching some assets, this method will overwrite them and clean the cache.

    05:16 If you're wondering why the cache is clean, let's first create the production service worker again. If you remember, this production service worker on the activate event which happens when another service worker gets installed, will delete all caches right before the other service worker takes place.