So erstellen Sie eine PWA von Grund auf mit HTML, CSS und JavaScript

Progressive Web-Apps sind eine Möglichkeit, das native App-Feeling einer herkömmlichen Web-App zu verleihen. Mit PWAs können wir unsere Website mit Funktionen für mobile Apps erweitern, die die Benutzerfreundlichkeit erhöhen und eine hervorragende Benutzererfahrung bieten.

In diesem Artikel erstellen wir eine PWA von Grund auf mit HTML, CSS und JavaScript. Hier sind die Themen, die wir behandeln werden:

  • Was ist eine progressive Web-App?
  • Markup
  • Styling
  • Daten mit JavaScript anzeigen
  • Web App Manifest
  • Was ist ein Servicemitarbeiter?
  • Cache die Assets
  • Holen Sie sich die Assets
  • Registrieren Sie den Servicemitarbeiter
  • Abschließende Gedanken
  • Nächste Schritte

Beginnen wir also mit einer wichtigen Frage: Was zum Teufel ist eine PWA?

Was ist eine progressive Web-App?

Eine progressive Web-App ist eine Web-App, die Benutzern mithilfe moderner Webfunktionen eine App-ähnliche Erfahrung bietet. Am Ende ist es nur Ihre normale Website, die in einem Browser mit einigen Verbesserungen ausgeführt wird. Es gibt Ihnen die Fähigkeit:

  • So installieren Sie es auf einem mobilen Startbildschirm
  • Um offline darauf zuzugreifen
  • Zugriff auf die Kamera
  • Push-Benachrichtigungen erhalten
  • Hintergrundsynchronisation durchführen

Und so viel mehr.

Um unsere herkömmliche Web-App in eine PWA umwandeln zu können, müssen wir sie jedoch ein wenig anpassen, indem wir eine Web-App-Manifestdatei und einen Servicemitarbeiter hinzufügen.

Machen Sie sich keine Sorgen um diese neuen Begriffe - wir werden sie unten behandeln.

Zuerst müssen wir unsere traditionelle Web-App erstellen. Beginnen wir also mit dem Markup.

Markup

Die HTML-Datei ist relativ einfach. Wir wickeln alles in das mainEtikett.

  • Im index.html
       Dev'Coffee PWA     

Dev'Coffee

  • Home
  • About
  • Blog

Und erstellen Sie eine Navigationsleiste mit dem navTag. Dann hält die divmit der Klasse .containerunsere Karten, die wir später mit JavaScript hinzufügen.

Nachdem wir das aus dem Weg geräumt haben, können wir es mit CSS gestalten.

Styling

Hier importieren wir wie gewohnt zunächst die benötigten Schriftarten. Dann werden wir einige Resets durchführen, um das Standardverhalten zu verhindern.

  • Im 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; } 

Dann begrenzen wir die mainmaximale Breite des Elements 900px, damit es auf einem großen Bildschirm gut aussieht.

Für die Navigationsleiste soll das Logo links und die Links rechts angezeigt werden. navNachdem wir das Tag zu einem Flex-Container gemacht haben, justify-content: space-between;richten wir es aus.

  • Im 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; } 

Wir haben mehrere Karten, daher wird das Containerelement als Raster angezeigt. Und mit grid-template-columns: repeat(auto-fit, minmax(15rem, 1fr))können wir unsere Karten jetzt so reagieren lassen, dass sie mindestens die 15remBreite verwenden, wenn genügend Platz vorhanden ist (und 1frwenn nicht).

Und damit sie schön aussehen wir den Schatteneffekt auf die doppelte .cardKlasse und Verwendung object-fit: coverauf .card--avatardas Bild , um zu verhindern Stretching.

Jetzt sieht es viel besser aus - aber wir haben noch keine Daten zu zeigen.

Lassen Sie es uns im nächsten Abschnitt beheben

Daten mit JavaScript anzeigen

Beachten Sie, dass ich große Bilder verwendet habe, deren Laden einige Zeit in Anspruch nimmt. Dies zeigt Ihnen am besten die Macht der Servicemitarbeiter.

Wie ich bereits sagte, wird die .containerKlasse unsere Karten halten. Deshalb müssen wir es auswählen.

  • Im 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" }, ] 

Dann erstellen wir eine Reihe von Karten mit Namen und Bildern.

  • Im 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-excited

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).

image-cache

Hopefully, you're still with me.

desesperate

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.

let-s-do-it

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.

we-did-it

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.

Thanks for reading this article.

You can check it out live here and the source code is here.

Read more of my articles on my blog

Next steps

Web Manifest Documentation

Service Worker Documentation

Web Manifest Generator

Browser Support