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A simple hack to serve service worker scripts from rails apps.
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A simple hack to serve service worker scripts from rails apps.

TLDR: Serves the webpack defined at app/javascript/packs/worker.js from /worker.js

Service workers can only intercept requests in the directory and subdirectory they are served from. Rails serves webpacked javascript from paths similar to /packs/js/application-abcd1234.js. Any service worker served from a path like this would only be able to operate on paths under /packs/js/; generally not what you want.

This gem lets you create a javascript pack for a service worker, and serve it from /worker.js.


Install the gem (see full instructions below).

Restart your server (so the gem's middleware can be added to the app).

Add a service worker pack by creating a file app/javascript/packs/worker.js. Here's a simple example to get started:

for (const name of ["install", "activate", "fetch"]) {
  self.addEventListener(name, event => console.log(event))

You also need to register your worker, adding something like this to app/javascript/packs/application.js:

if ("serviceWorker" in navigator) {
  window.addEventListener("load", function () {


Add this line to your application's Gemfile:

gem 'rails-pwa'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rails-pwa

How it works

This gem installs a very simple piece of Rack::Middleware into your app, which intercepts all requests to /worker.js and either:

  • In development: Rewrites and forwards the request to the rails app (where the usual webpacker magic will occure)
  • In other environments: Serves the precompiled worker.js pack directly from /public/packs/js/. N.B. You may want to use some other form of url rewriting in production, depending on how your app is deployed.


The gem is available as open source under the terms of the MIT License.

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