Sådan oprettes en PWA fra bunden med HTML, CSS og JavaScript

Progressive webapps er en måde at bringe den indfødte app-følelse til en traditionel webapp. Med PWA'er kan vi forbedre vores hjemmeside med mobilapp-funktioner, der øger brugervenligheden og tilbyder en god brugeroplevelse.

I denne artikel skal vi opbygge en PWA fra bunden med HTML, CSS og JavaScript. Her er de emner, vi dækker:

  • Hvad er en progressiv webapp?
  • Markup
  • Styling
  • Vis data med JavaScript
  • Webappmanifest
  • Hvad er en servicearbejder?
  • Cache aktiverne
  • Hent aktiverne
  • Registrer servicearbejderen
  • Afsluttende tanker
  • Næste skridt

Så lad os komme i gang med et vigtigt spørgsmål: Hvad pokker er en PWA?

Hvad er en progressiv webapp?

En progressiv webapp er en webapp, der leverer en app-lignende oplevelse til brugerne ved hjælp af moderne webfunktioner. I sidste ende er det bare dit almindelige websted, der kører i en browser med nogle forbedringer. Det giver dig muligheden:

  • For at installere det på en mobil startskærm
  • For at få adgang til det, når du er offline
  • For at få adgang til kameraet
  • For at få push-underretninger
  • At udføre baggrundssynkronisering

Og så meget mere.

For at kunne omdanne vores traditionelle webapp til en PWA er vi dog nødt til at justere den lidt ved at tilføje en webapp-manifestfil og en servicearbejder.

Du skal ikke bekymre dig om disse nye vilkår - vi dækker dem nedenfor.

Først skal vi bygge vores traditionelle webapp. Så lad os starte med markeringen.

Markup

HTML-filen er relativt enkel. Vi indpakker alt i mainkoden.

  • I index.html
       Dev'Coffee PWA     

Dev'Coffee

  • Home
  • About
  • Blog

Og opret en navigationslinje med navtagget. Derefter holder divklassen .containervores kort, som vi tilføjer senere med JavaScript.

Nu hvor vi har fået det ud af vejen, lad os style det med CSS.

Styling

Her starter vi som sædvanlig med at importere de skrifttyper, vi har brug for. Så foretager vi nogle nulstillinger for at forhindre standardadfærd.

  • I css/style.css
@import url("//fonts.googleapis.com/css?family=Nunito:400,700&display=swap"); * { margin: 0; padding: 0; box-sizing: border-box; } body { background: #fdfdfd; font-family: "Nunito", sans-serif; font-size: 1rem; } main { max-width: 900px; margin: auto; padding: 0.5rem; text-align: center; } nav { display: flex; justify-content: space-between; align-items: center; } ul { list-style: none; display: flex; } li { margin-right: 1rem; } h1 { color: #e74c3c; margin-bottom: 0.5rem; } 

Derefter begrænser vi mainelementets maksimale bredde for 900pxat få det til at se godt ud på en stor skærm.

For navbaren vil jeg have logoet til venstre og linkene til højre. Så for navtagget, efter at have gjort det til en flexcontainer, bruger vi justify-content: space-between;til at justere dem.

  • I css/style.css
.container { display: grid; grid-template-columns: repeat(auto-fit, minmax(15rem, 1fr)); grid-gap: 1rem; justify-content: center; align-items: center; margin: auto; padding: 1rem 0; } .card { display: flex; align-items: center; flex-direction: column; width: 15rem auto; height: 15rem; background: #fff; box-shadow: 0 10px 20px rgba(0, 0, 0, 0.19), 0 6px 6px rgba(0, 0, 0, 0.23); border-radius: 10px; margin: auto; overflow: hidden; } .card--avatar { width: 100%; height: 10rem; object-fit: cover; } .card--title { color: #222; font-weight: 700; text-transform: capitalize; font-size: 1.1rem; margin-top: 0.5rem; } .card--link { text-decoration: none; background: #db4938; color: #fff; padding: 0.3rem 1rem; border-radius: 20px; } 

Vi har flere kort, så for containerelementet vises det som et gitter. Og med grid-template-columns: repeat(auto-fit, minmax(15rem, 1fr))kan vi nu gøre vores kort lydhøre, så de bruger mindst 15rembredde, hvis der er plads nok (og 1frhvis ikke).

Og for at få dem til at se pæne ud fordobles vi skyggeeffekten på .cardklassen og bruger object-fit: coverden for .card--avatarat forhindre, at billedet strækker sig.

Nu ser det meget bedre ud - men vi har stadig ikke data at vise.

Lad os ordne det i næste afsnit

Vis data med JavaScript

Bemærk, at jeg brugte store billeder, der tager noget tid at indlæse. Dette vil vise dig på den bedste måde styrken fra servicearbejdere.

Som jeg sagde tidligere, .containerholder klassen vores kort. Derfor er vi nødt til at vælge det.

  • I js/app.js
const container = document.querySelector(".container") const coffees = [ { name: "Perspiciatis", image: "images/coffee1.jpg" }, { name: "Voluptatem", image: "images/coffee2.jpg" }, { name: "Explicabo", image: "images/coffee3.jpg" }, { name: "Rchitecto", image: "images/coffee4.jpg" }, { name: " Beatae", image: "images/coffee5.jpg" }, { name: " Vitae", image: "images/coffee6.jpg" }, { name: "Inventore", image: "images/coffee7.jpg" }, { name: "Veritatis", image: "images/coffee8.jpg" }, { name: "Accusantium", image: "images/coffee9.jpg" }, ] 

Derefter opretter vi en række kort med navne og billeder.

  • I js/app.js
const showCoffees = () => { let output = "" coffees.forEach( ({ name, image }) => (output += ` 

${name}

Taste `) ) container.innerHTML = output } document.addEventListener("DOMContentLoaded", showCoffees)

With this code above, we can now loop through the array and show them on the HTML file. And to make everything work, we wait until the DOM (Document Object Model) content finishes loading to run the showCoffees method.

We've done a lot, but for now, we just have a traditional web app. So, let's change that in the next section by introducing some PWA features.

super begejstret

Web App Manifest

The web app manifest is a simple JSON file that informs the browser about your web app. It tells how it should behave when installed on the user's mobile device or desktop. And to show the Add to Home Screen prompt, the web app manifest is required.

Now that we know what a web manifest is, let's create a new file named manifest.json (you have to name it like that) in the root directory. Then add this code block below.

  • In manifest.json
{ "name": "Dev'Coffee", "short_name": "DevCoffee", "start_url": "index.html", "display": "standalone", "background_color": "#fdfdfd", "theme_color": "#db4938", "orientation": "portrait-primary", "icons": [ { "src": "/images/icons/icon-72x72.png", "type": "image/png", "sizes": "72x72" }, { "src": "/images/icons/icon-96x96.png", "type": "image/png", "sizes": "96x96" }, { "src": "/images/icons/icon-128x128.png", "type": "image/png","sizes": "128x128" }, { "src": "/images/icons/icon-144x144.png", "type": "image/png", "sizes": "144x144" }, { "src": "/images/icons/icon-152x152.png", "type": "image/png", "sizes": "152x152" }, { "src": "/images/icons/icon-192x192.png", "type": "image/png", "sizes": "192x192" }, { "src": "/images/icons/icon-384x384.png", "type": "image/png", "sizes": "384x384" }, { "src": "/images/icons/icon-512x512.png", "type": "image/png", "sizes": "512x512" } ] } 

In the end, it's just a JSON file with some mandatory and optional properties.

name: When the browser launches the splash screen, it will be the name displayed on the screen.

short_name: It will be the name displayed underneath your app shortcut on the home screen.

start_url: It will be the page shown to the user when your app is open.

display: It tells the browser how to display the app. There are several modes like minimal-ui, fullscreen, browser etc. Here, we use the standalone mode to hide everything related to the browser.

background_color: When the browser launches the splash screen, it will be the background of the screen.

theme_color: It will be the background color of the status bar when we open the app.

orientation: It tells the browser the orientation to have when displaying the app.

icons: When the browser launches the splash screen, it will be the icon displayed on the screen. Here, I used all sizes to fit any device's preferred icon. But you can just use one or two. It's up to you.

Now that we have a web app manifest, let's add it to the HTML file.

  • In index.html (head tag)

As you can see, we linked our manifest.json file to the head tag. And add some other links which handle the iOS support to show the icons and colorize the status bar with our theme color.

With that, we can now dive into the final part and introduce the service worker.

What is a Service Worker?

Notice that PWAs run only on https because the service worker can access the request and handle it. Therefore security is required.

A service worker is a script that your browser runs in the background in a separate thread. That means it runs in a different place and is completely separate from your web page. That's the reason why it can't manipulate your DOM element.

However, it's super powerful. The service worker can intercept and handle network requests, manage the cache to enable offline support or send push notifications to your users.

wow

S0 let's create our very first service worker in the root folder and name it serviceWorker.js (the name is up to you). But you have to put it in the root so that you don't limit its scope to one folder.

Cache the assets

  • In serviceWorker.js
const staticDevCoffee = "dev-coffee-site-v1" const assets = [ "/", "/index.html", "/css/style.css", "/js/app.js", "/images/coffee1.jpg", "/images/coffee2.jpg", "/images/coffee3.jpg", "/images/coffee4.jpg", "/images/coffee5.jpg", "/images/coffee6.jpg", "/images/coffee7.jpg", "/images/coffee8.jpg", "/images/coffee9.jpg", ] self.addEventListener("install", installEvent => { installEvent.waitUntil( caches.open(staticDevCoffee).then(cache => { cache.addAll(assets) }) ) }) 

This code looks intimidating first but it just JavaScript (so don't worry).

We declare the name of our cache staticDevCoffee and the assets to store in the cache. And to perform that action, we need to attach a listener to self.

self is the service worker itself. It enables us to listen to life cycle events and do something in return.

The service worker has several life cycles, and one of them is the install event. It runs when a service worker is installed. It's triggered as soon as the worker executes, and it's only called once per service worker.

When the install event is fired, we run the callback which gives us access to the event object.

Caching something on the browser can take some time to finish because it's asynchronous.

So to handle it, we need to use waitUntil() which, as you might guess, waits for the action to finish.

Once the cache API is ready, we can run the open() method and create our cache by passing its name as an argument to caches.open(staticDevCoffee).

Then it returns a promise, which helps us store our assets in the cache with cache.addAll(assets).

billed-cache

Hopefully, you're still with me.

fortvivlet

Now, we've successfully cached our assets in the browser. And the next time we load the page, the service worker will handle the request and fetch the cache if we are offline.

So, let's fetch our cache.

Fetch the assets

  • In serviceWorker.js
self.addEventListener("fetch", fetchEvent => { fetchEvent.respondWith( caches.match(fetchEvent.request).then(res =>  return res ) ) }) 

Here, we use the fetch event to, well, get back our data. The callback gives us access to fetchEvent. Then we attach respondWith() to prevent the browser's default response. Instead it returns a promise because the fetch action can take time to finish.

And once the cache ready, we apply the caches.match(fetchEvent.request). It will check if something in the cache matches fetchEvent.request. By the way, fetchEvent.request is just our array of assets.

Then, it returns a promise. And finally, we can return the result if it exists or the initial fetch if not.

Now, our assets can be cached and fetched by the service worker which increases the load time of our images quite a bit.

And most important, it makes our app available in offline mode.

But a service worker alone can't do the job. We need to register it in our project.

Lad os gøre det

Register the Service Worker

  • In js/app.js
if ("serviceWorker" in navigator) { window.addEventListener("load", function() { navigator.serviceWorker .register("/serviceWorker.js") .then(res => console.log("service worker registered")) .catch(err => console.log("service worker not registered", err)) }) } 

Here, we start by checking if the serviceWorker is supported by the current browser (as it's still not supported by all browsers).

Then, we listen to the page load event to register our service worker by passing the name of our file serviceWorker.js to navigator.serviceWorker.register() as a parameter to register our worker.

With this update, we have now transformed our regular web app to a PWA.

vi gjorde det

Final thoughts

Throughout this article, we have seen how amazing PWAs can be. By adding a web app manifest file and a service worker, it really improves the user experience of our traditional web app. This is because PWAs are fast, secure, reliable, and – most importantly – they support offline mode.

Many frameworks out there now come with a service worker file already set-up for us. But knowing how to implement it with Vanilla JavaScript can help you understand PWAs.

And you can go even further with service workers by caching assets dynamically or limiting the size of your cache and so on.

Tak, fordi du læste denne artikel.

Du kan tjekke det live her, og kildekoden er her.

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