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Ship PWA Guided by Lighthouse

Photo by Robert Wiedemann

Nowadays, PWA is so hyped. All the cool kids are implementing PWA, or on the way to implement it. It’s like a magic box, they said, what contains ultimate happiness for users. Wow it sounds awesome, right? How is it possible that I could miss this opportunity to stay as a member of the cool kids club?

What is actually PWA?

According to Google, Progressive Web Apps are user experiences that have the reach of the web, and are [1]:

  • Reliable: Load instantly and never show the downasaur, even in uncertain network conditions.
  • Fast: Respond quickly to user interactions with silky smooth animations and no janky scrolling.
  • Engaging: Feel like a natural app on the device, with an immersive user experience.

Personally, I prefer another alternative version because it uses one word to represent PWA: F.I.R.E 🔥 Fast, Integrated, Reliable and Engaging. [2]:

Many people are confused by the fancy term of PWA, like this: Google’s continued use of the term “quality” in describing things leaves me with a ton of confusion… [3]

To be honest, PWA is not a new technology at all. It’s a new web app quality standard for web experiences [4].

How to get my app on F.I.R.E.?

Are you sold by the idea of PWA? I’ll buy it. Because I would do whatever I could to improve the user experience. So, I decided to optimize my blog site for reaching PWA standard.

Step 1: Run a performance audit

Lighthouse is a must-have tool to audit web app performance. Lighthouse is already integrated in the recent versions of Chrome and Chromium, as a part of DevTools, which makes it super convenient to use:

Inspect -> Audits -> Perform an audit...

Step 2: Read audit report carefully

After running an audit in Lighthouse, it will provide a detailed report. First, it shows the overall scores:

Overview of the first Lighthouse audit result

I’m not surprised by this result, not at all. These numbers are making people feel good when they have greens. Besides that, I would suggest to ignore them.

When continuing reading the report, I find the interesting parts: failed audits. It’s a nicely organized To-Do list, especially the Learn more links which open documents to explain why the audit is important and how to pass the audit.

Failed audits for PWA section

Step 3: Get hands dirty

It’s time to handle all failed cases one by one. Most of them are rather easy to solve by following “Learn more” tutorials. Only “Does not register a Service Worker” and “Does not respond with a 200 when offline” are relatively tough. I’d like to share some tips, which come from my Aha moments.

A working service worker has 4 essential parts:

  • manifest.json: It’s a json file located in / web app root directory:
  "short_name": "Kevin",
  "name": "Kevin Cui",
  "icons": [
      "sizes": "512x512",
      "type": "image/png"
  "start_url": "/",
  "background_color": "#000",
  "theme_color": "#000",
  "display": "standalone"
  • Link manifest.json in index.html:
<link rel="manifest" href="/manifest.json">
  • Service worker js: It must be created in web app root directory, alongside with manifest.json. Here is an example of the service worker called sw.js:
var CACHE_NAME = 'kevin-site';
var urlsToCache = [

self.addEventListener('install', function(event) {
  // Perform install steps
      .then(function(cache) {
        console.log('Opened cache');
        return cache.addAll(urlsToCache);

self.addEventListener('fetch', function(event) {
      .then(function(response) {
        if (response) {
          return response;

        var fetchRequest = event.request.clone();

        return fetch(fetchRequest).then(
          function(response) {
            if(!response || response.status !== 200 || response.type !== 'basic') {
              return response;

            var responseToCache = response.clone();

              .then(function(cache) {
                cache.put(event.request, responseToCache);

            return response;
  • A piece of JavaScript code to register service worker in index.html:
if ('serviceWorker' in navigator) {
  .then(function(registration) {
    console.log("Service Worker Registered", registration);
  .catch(function(err) {
    console.log("Service Worker Failed to Register", err);

For more details of all these parts above, there is a good tutorial to follow: Add Your Web App to a User’s Home Screen and a good example of PWA app to check its source code: airhorn

My app is on 🔥!

Once the dirty jobs are well done, it’s time to run another performance audit. Although I know all score numbers are meaningless without contexts, it still feels damn awesome when I see all greens, right?

Another overview of Lighthouse audit result

Surprisingly, Firefox now starts to support PWA as well.

What else?

I have to admit that it’s not hard to pass Lighthouse audit checks. However, I must keep in mind that it’s just one step of improving web app performance towards the goal of “better user experience”. Many steps ahead I still need to move on.

What’s your opinion about PWA? Would you like to ship your app guided by Lighthouse? And join the cool kids club?

[1] Google: Progressive Web Apps
[2] Ewa Gasperowicz: From Website to Progressive Web App
[3] Ben Halpern: What the heck is a “Progressive Web App”? Seriously.
[4] Thao Tran and Chris Wilson: The New Bar for Web Experiences