Service Worker Precache

As we have mentioned in Service Worker section, service workers act as proxies intercepting requests between the browser and the server.

Since we are going to add PWA to your application, we need to configure the service worker so that your application can work offline. To do this, we need to configure the service worker's precache manifest, which will include all the resources of your application (basically we need to instruct the service worker what resources to store in cache storage so that it can be used for network requests interception and when the application is offline).

Network requests interception

You can also configure how to control the network requests interception for any of your application resources.

You can find more information on Workbox - Caching Strategies.

Once the application registers the service worker, the browser will try to install it downloading all the resources in the service worker's precache manifest. Once all the resources downloaded and stored in the cache storage by the browser, it will try to activate the service worker to take the control of the application.

TIP

The browser will only download all the resources in the service worker's precache manifest if the service worker is not installed (first time the user visit your application) or if there is a new version of your application (if you change some resource in your application, the service worker will also change once you build the application, since its precache manifest is modified to include your changes).

In any case, the browser will always download all the resources in a background thread and not in the main browser thread, this way people can use the application while the browser is trying to install the service worker.

You can check this website or the VueUse docs site in a private window, just open Network Tab on dev tools before visiting the sites: the browser will start download all the resources while you navigate the site.

Precache Manifest

Since vite-plugin-pwa plugin uses workbox-build node library to build the service worker, it will only include css, js and html resources in the manifest precache (check the globPatterns entry in GlobPartial).

workbox-build node library is file based, that is, it will traverse the build output folder of your application. Vite will generate your build in the dist folder, and so, workbox-build will traverse the dist folder adding all resources found in it to the service worker's precache manifest.

If you need to include another resource types, you will need to add them to the globPatterns entry. Depending on the strategy configured in the vite-plugin-pwa plugin configuration, you will need to add it under the workbox or injectManifest configuration option.

You can find more information in the Static assets handling section.

For example, if you need to add ico, png and svg resources in the example from the Configuring vite-plugin-pwa - Guide section, you will need to add globPatterns under workbox entry, since we're using the default vite-plugin-pwa strategy (generateSW):

import { VitePWA } from 'vite-plugin-pwa'

export default defineConfig({
  plugins: [
    VitePWA({
      registerType: 'autoUpdate',
      workbox: {
        globPatterns: ['**/*.{js,css,html,ico,png,svg}']
      }
    })
  ]
})