Workbox is a collection of flexible abstractions that let us do hard things more simply

Indrek Lasn
Jun 29 · 3 min read
PWA Workbox —

Adding pre-caching, caching strategies, routing, and background sync for your progressive web app is complicated.

Workbox is a collection of flexible abstractions that let us do hard things more simply.

Workbox: Flexible PWA Libraries (Chrome Dev Summit 2017)

In a nutshell, Workbox lets us do the following, easily:

  • Serve cache-first images, HTML, and CSS styles to increase web apps’ performance.
  • Automatic cache cleanups, and updates.
  • Runtime caching.
  • Strategies.
  • Request routing.
  • Background sync.

Getting Started With Workbox

Workbox gives us a handy command line tool out of the box.

yarn add workbox-cli

Once we have the CLI, run the wizard. Enter the relative paths for your app.

npx workbox wizard
Running workbox wizard

You should see a new file workbox-config.js appear at the root of your project.

The config file defines our root directory, which files to cache and where our sw.js located.

Generate the Service Worker File

generating service worker file
npx workbox generateSW workbox-config.js

You should see thesw.js file appear, which might look like something like this:

It’s a long file, but basically, it installs workbox and tells the browser which files to cache.

You can remove the service-worker.js file and register our new service worker — sw.js.

If we relaunch and open our browser, we should have offline support, caching and fetching cached assets enabled now.

workbox PWA

Click on the offline box and try refreshing. If you check the Cache Storage tab, you should see everything stored in the cache. Magic!

Workbox precache

As of now, we can’t modify the generated file, because any change we make will be overwritten as soon as we re-generate the service worker file.

If you would like to modify the sw.js, here’s how you can do it:

Create a new file called src-sw.js with the following contents. The content of the src-sw.js file will be injected inside the sw.js file.

Tell the original sw.js file where the src-sw.js is located.

swSrc property

Finally, run the command:

npx workbox injectManifest

Now we should see the console.log show up in the sw.js file.

Injecting options to sw.js file
When to use injectManifest

Workbox can do much, much more. Please read the documentation to try out different features.

Workbox full documentation —

Where to go from here?

I highly recommend building stuff. Building stuff is by far the best way to get good at things, here’s a list of fun apps to build.

If you want to learn about progressive web apps in-depth, I’d suggest reading through the “Building Progressive Web Apps: Bringing the Power of Native to the Browser” book.

Source Code

Here’s the source code for this chapter.

Thanks for reading!

Better Programming

Advice for programmers.

Indrek Lasn

Written by

The future is here. Invest in yourself. I was a corporate drone, and now I’m a free man. So can you. Follow me on Twitter @

Better Programming

Advice for programmers.

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