Progressive Web App (PWA) - how do you build an app that works offline?

In a world dominated by smartphones, the line between websites and native mobile apps is blurring faster than ever. Traditional apps need to be downloaded from app stores (App Store, Google Play), which for many users is an insurmountable barrier. The solution to this problem is How to build a progressive web app (PWA) an app that combines the lightness of a web page with the features familiar from iOS or Android? PWAs are the future of the internet, allowing you to install a website on your home screen, send push notifications and – most importantly – use it without an internet connection.

The three pillars of PWAs: The foundations of a modern application

For your website to be recognised as a fully-fledged PWA, it must meet three technical requirements. These are what define its uniqueness and „progressive” nature.

1. HTTPS protocol: Security is paramount. As PWAs make use of powerful APIs, Google requires an encrypted connection to prevent man-in-the-middle attacks.
2. Web App Manifest: A JSON file that tells the browser how your app should look once it has been installed (icons, launch colours, full-screen mode).
3. Service Worker: The heart of a PWA. This is a script that runs in the background, independently of the webpage, and manages the cache and network traffic.

Understanding these mechanisms is the first step towards building efficient solutions. You can find out more about optimisation in this post: Optimising the performance of web applications.

Web App Manifest – make your website look like an app

The first practical step in this area How to build a progressive web app (PWA) is to create a file manifest.json. This is where you define your product’s visual identity.

The key points in the manifesto:

• name and short_name: The name displayed beneath the icon on the desktop.
• icons: A set of graphics in various resolutions (minimum 192×192 and 512×512 pixels).
• start_url: The page on which the application should open when it is launched.
• display: Setting standalone will make the browser interface (address bar) disappear, giving the impression of a native app.
• background_colour: The colour of the splash screen.

Service Workers and the magic of offline mode

This is the most difficult, but also the most rewarding stage. A Service Worker acts as a proxy between your application and the server. When a user loses their connection, the Service Worker can serve them data previously stored in the cache (Cache Storage).

You can read more about their technical implementation here: Service Workers – how do they work and what are they used for?.

During development, it is worth implementing one of the tried-and-tested caching strategies:

• Cache First: Ideal for static resources (logos, CSS). The application first checks the cache, and if nothing is found there, it retrieves the data from the internet.
• Network First: Suitable for data that needs to be up to date. The system attempts to retrieve data from the network and, in the event of an error, displays the last saved version.
• Stale-While-Revalidate: It serves the cached version straight away, but at the same time downloads an update from the internet in the background for future use.

Push notifications and advanced APIs

A PWA allows you to build engagement through notifications, even when the browser is closed. This is achieved by using Push API and Notification API. In practice, they are most often integrated with services such as Firebase Cloud Messaging (FCM), which enables the mass sending of messages about promotions or news.

Modern PWA applications also have access to features that were previously reserved solely for native systems, such as:

• Geolocation,
• Access to the camera and microphone,
• Content sharing (Web Share API),
• Payments (Payment Request API).

You can find official support and documentation for these solutions at MDN – Service Workers API and in a comprehensive guide web.dev – A Guide to PWAs.

Testing and deployment – the Lighthouse tool

Once your app is ready, you need to check that it meets all the standards. The best tool for this is Google Lighthouse, built into the Chrome developer tools (the ‘Audits’ tab). Lighthouse will check the validity of the manifest, performance on a slow connection, and whether your site switches to offline mode correctly.

PWAs have a huge advantage in mobile search results – Google favours websites that offer a native experience. Adding an offline mode significantly improves this metric INP (Interaction to Next Paint), because the app does not „freeze” when there are network issues, responding instantly to the user’s actions.

Help shape the future of the internet today

Understanding How to build a progressive web app (PWA) A professional product gives you a huge competitive advantage. A PWA isn’t just about cost savings (one codebase for all platforms); above all, it delivers better conversion rates and greater user satisfaction, as users value speed and the fact that the experience isn’t affected by connection quality.

At 4ADStudio, we design PWA apps that form the foundation of modern businesses. We help companies make the transition from traditional websites to dynamic solutions that are always at the customer’s fingertips.

Is your website loading too slowly on mobile phones? Do you want your customers to be able to use your services even without an internet connection? Get in touch with us – we’ll build a PWA app for you that will revolutionise your interaction with users and take your visibility on Google to a whole new level!