Simple plugin for injecting the precache files and setting up the local workbox files.

snowpack-workbox-plugin.js

const { injectManifest, InjectManifestConfig, copyWorkboxLibraries } = require('workbox-build')
const rimraf = require('rimraf')
const { convertCompilerOptionsFromJson } = require('typescript')
const prependFile = require('prepend-file')
const { isNil } = require('ramda')
const { isEmpty } = require('ramda')
const { map } = require('ramda')

/**
 * Injects the Manifest for the Service worker
 * @param {*} snowpackConfig
 * @param {{workbox: InjectManifestConfig, exclude: string[] }} pluginOptions
 * @returns
 */
module.exports = function (snowpackConfig, { exclude, workbox }) {
  return {
    name: 'workbox-plugin',
    async optimize({ buildDirectory, log }) {
      try {
        const libPath = await copyWorkboxLibraries(buildDirectory)
        const importLibsTemplate = `// import ${libPath}
importScripts('/${libPath}/workbox-sw.js')
workbox.setConfig({
  modulePathPrefix: '/${libPath}/',
  debug: false
})

`
        log('Removing the *.dev.* files from the workbox source libraries')
        rimraf.sync(`${buildDirectory}/${libPath}/*.dev.*`)

        if (!isNil(exclude) || !isEmpty(exclude)) {
          map((e) => {
            log(`Removing the ${e} files from the workbox source libraries`)
            rimraf.sync(`${buildDirectory}/${libPath}/workbox-${e}*`)
          }, exclude)
        }

        const { count, size } = await injectManifest({
          ...workbox,
        })

        await prependFile(workbox.swDest, importLibsTemplate)

        log(
          `Generated ${workbox.swDest}, which will precache ${count} files, totaling ${(
            size / 1000
          ).toFixed(2)} KB.`,
        )
      } catch (error) {
        throw new Error(error)
      }

      log('Now you have service-worker 🎉')
    },
  }
}

snowpack.config.js

// Snowpack Configuration File
// See all supported options: https://www.snowpack.dev/reference/configuration
const path = require("path");

/** @type {import("snowpack").SnowpackUserConfig } */
module.exports = {
  mount: {
    public: { url: "/", static: true, resolve: false },
    src: { url: "/dist" },
  },
  plugins: [
    [
      "./plugins/workbox.js",
      {
        workbox: {
          globDirectory: "build/",
          globPatterns: ["**/*.{html,json,js,css}"],
          swDest: path.resolve(__dirname, "build/service-worker.js"),
          swSrc: path.resolve(__dirname, "build/service-worker.js"),
        },
        exclude: ["offline-ga"],
      },
    ],
  ],
};