Progressive Web Apps

Preact is an excellent choice for Progressive Web Apps that wish to load and become interactive quickly. Preact CLI codifies this into an instant build tool that gives you a PWA with a 100 Lighthouse score right out of the box.

  1. Loads less script

    Preact's small size is valuable when you have a tight loading performance budget. On average mobile hardware, loading large bundles of JS leads to longer load, parse and eval times. This can leave users waiting a long time before they can interact with your app. By trimming down the library code in your bundles, you load quicker by shipping less code to your users.

  2. Faster time to interactivity

    If you're aiming to be interactive in under 5s, every KB matters. Switching React for Preact in your projects can shave multiple KBs off and enable you to get interactive in one RTT. This makes it a great fit for Progressive Web Apps trying to trim down as much code as possible for each route.

  3. A building block that works great with the React ecosystem

    Whether you need to use React's server-side rendering to get pixels on the screen quickly or use React Router for navigation, Preact works well with many libraries in the ecosystem.

This site is a PWA

In fact, the site you're on right now is a Progressive Web App!. Here it is getting interactive in under 5 seconds in a trace from a Nexus 5X over 3G:

A DevTools Timeline trace of the site on a Nexus 5X

Static site content is stored in the (Service Worker) Cache Storage API enabling instant loading on repeat visits.

Performance tips

While Preact is a drop-in that should work well for your PWA, it can also be used with a number of other tools and techniques. These include:

  1. Code-splitting breaks up your code so you only ship what the user needs for a page. Lazy-loading the rest as needed improves page load times. Supported via webpack or Rollup.

  2. Service Worker caching allows you to offline cache static and dynamic resources in your app, enabling instant loading and faster interactivity on repeat visits. Accomplish this with Workbox

  3. PRPL encourages preemptively pushing or pre-loading assets to the browser, speeding up the load of subsequent pages. It builds on code-splitting and SW caching.

  4. Lighthouse allows you to audit the performance and best practices of your Progressive Web App so you know how well your app performs.

Preact CLI

Preact CLI is the official build tool for Preact projects. It's a single dependency command line tool that bundles your Preact code into a highly optimized Progressive Web App. It aims to make all of the above recommendations automatic, so you can focus on writing great Components.

Here are a few things Preact CLI bakes in:

  • Automatic, seamless code-splitting for your URL routes
  • Automatically generates and installs a ServiceWorker
  • Generates HTTP2/Push headers (or preload meta tags) based on the URL
  • Pre-rendering for a fast Time To First Paint
  • Conditionally loads polyfills if needed

Since Preact CLI is internally powered by Webpack, you can define a preact.config.js and customize the build process to suit your needs. Even if you customize things, you still get to take advantage of awesome defaults, and can update as new versions of preact-cli are released.