I spent some time today and hacked together a simple Jekyll plugin to automatically generate a service worker with Google Workbox, with minimal overhead / effort. I had previously used the jekyll-pwa-plugin, which is awesome, but it’s doing a bit too much for my taste:

1. Local copy of the workbox distribution rather than fetching it from the Google CDN.
2. Generates both the actual service sw.js as well as a loader script sw-register.js, which also emits a sw.update event, which I don’t need.
3. Inserts a <script> snippet into each .html file generated that loads sw-register.js, prepending the current timestamp to the URL to avoid caching.

The sw-register.js itself also uses a timestamped URL to load the sw.js file. All of this is actually unnecessary since I have configured my server to respond with Cache-Control: no to sw.js requests (and even that is no longer necessary as I learned today), plus I already have a main.js that runs during page load, so I’d rather do the service worker registration there via the common sequence:

if ('serviceWorker' in navigator) {
  window.addEventListener('load', function() {
    navigator.serviceWorker.register('/sw.js');
  });
}

The only thing I actually need is the ability to do the precaching automatically and inject the right call to workbox.precaching.precacheAndRoute() into the final sw.js, plus the convenience of adding the appropriate importScript()call in the beginning.

So I created the jekyll-workbox-plugin (ruby gem), which does that — and only that. I hope you’ll find it useful. You can find documentation regarding Installation and Getting Started on the project page. In a nutshell, you add gem 'jekyll-workbox-plugin' to the jekyll_plugin group in your Gemfile:

source 'https://rubygems.org'

gem 'jekyll'

group :jekyll_plugins do
  gem 'jekyll-workbox-plugin'
end

and run bundle to install the gem. After the plugin has been installed successfully, add the following lines to your _config.yml in order to tell Jekyll to use the plugin:

plugins:
  - jekyll-workbox-plugin

Finally you need to create a template sw.js file, which looks something like this:

// sw.js

// set names for both precache & runtime cache
workbox.core.setCacheNameDetails({
    prefix: 'my.site.tld',
    suffix: 'v1',
    precache: 'precache',
    runtime: 'runtime-cache'
});

// let Workbox handle our precache list
// NOTE: This will be populated by jekyll-workbox-plugin.
workbox.precaching.precacheAndRoute([]);

It’s important to have the workbox.precaching.precacheAndRoute([]) in there, which jekyll-workbox-plugin will automatically populate.