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A 5 minute intro to Workbox 3.0

In this article, I’m only going to focus on using workbox to generate the service worker file for your application.

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Workbox 3.0.0 was released on March 14 🎉

The approach that I take when teaching new technologies is to go a bit low level while isolating concepts.

We’re omitting the build step here to make sure you understand how workbox works.

So to follow along this tutorial, start by cloning this repository and installing its dependencies:

The only dependency that we’re installing is http-server which will let you serve your application in the browser.

This is the folder structure that we have at the moment:

Let’s start by installing the latest pre-release version of Workbox-cli

I prefer installing libraries locally rather than globally in order to avoid unexpected problems when working on multiple projects.

So because we installed workbox locally, you can now invoke it by using npx

npx workbox (rather than justworkbox).

The first Workbox command that we’re going to go through is wizard.

workbox wizard scans your directory and asks you a series of questions in order to generate a workbox-config.js that will be used later on whenever you invoke workbox.

and now workbox will ask you a series of questions.

Answer with yes to all the questions, since all the defaults make sense and you can simply edit the file later on if you need to.

You will now have a workbox-config.js at the root, containing the below configuration:

This workbox command will read your workbox-config.js and generate a service-worker file that pre-caches files based on the globPatterns that we got from workbox wizard: **/*.{css,html,js}.

Now that the service worker file has been generated, we have to register it.

So let’s go into the index.html and add the following piece of code before the closing tag of the body:

Workbox will also request the index.html, app.css & app.js with a specific workbox-cache-buest parameter to make sure you get the latest version of your assets.

You can also inspect these pre-cached assets by going into Application > Cache Storage (you may need to right-click & refresh) > workbox-precache.

In this revamped dev tools page, you can see the cached assets alongside their content which is shown in the Preview tab.

Go back to the Network tab and make yourself Offline.

Reload the page and you will see that you still get a response for the index.html, app.js & app.css. That’s because they have been pre-cached and are being served even when offline.

As you can see, the entire service worker file is now generated by Workbox. But what if you want to change one thing? What if you want to add one line? Add offline analytics?

You cannot change the generated file because any change you make will be overwritten as soon as you re-generate the service worker file.

This is why you have to use injectManifest whenever you want to stay in control of your service-worker file and let Workbox generate part of it.

So we need to have a source service worker file, that will be used to generate the final service worker.

Let’s create src-sw.js file at the root of your project and write the following code in side of it:

So we’re importing workbox from CDN, adding some custom code (for now it’s simply a console log) and then adding a placeholder: workbox.precaching.precacheAndRoute([]); .

Workbox will generate the precaching array and inject it into this line of code: workbox.precaching.precacheAndRoute([]); while keeping the rest of the code intact.

Now in workbox-config.js, add the following line:

You should end up having this configuration in your workbox-config.js:

Now simply run: npx workbox injectManifest

And here’s the generated service worker that you’ll get:

We’ve done pre-caching so far, where we instruct workbox to add some resources to the cache because we will be using them later on.

But what about dynamic resources? What if you call a specific API and you want to cache its response?

Here comes the job of Workbox routing which allows you to define a regular expression that matches a specific request with a strategy.

You could define your own strategy but most of the times you’d use one of these 3 that are already existing:

new RegExp('https://jsonplaceholder.typicode.com/users').

Now simply register the route as below in your src-sw.js file by placing it under the console.log('this is my custom service worker');.

And let’s regenerate the service worker file by running npx workbox injectManifest.

I encourage you to take a look at the newly generated service worker in build/sw.js just to make sure that you strengthen these concepts in your head.

If you stopped serving your app, you can do it again by running npm run serve.

Then reload the page once in order to get the new service worker, then reload it again in order to cache the response of /users in the cache (using the new service worker code) and then go offline.

Checkout how the fetch request to /users is being served from the cache.

With that, you’re ready to dive deeper into workbox and build awesome PWAs.

Checkout my interactive courses:

Are you looking for an intro to Progressive Web Apps before you get started with Workbox? Then checkout the video series below!

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