How to Build Offline Web Applications
Tags: webdev, javascript, tutorial, programming
Published: 2023-02-16 23:34:47



With the increasing prevalence of mobile devices and unreliable network connections, it’s more important than ever to ensure that web applications can function even when a user is offline.</p>
<p class="graf graf--p">Additionally, users expect web applications to be reliable and fast, with minimal downtime and interruptions.</p>
<p class="graf graf--p">One way to achieve this is by building Progressive Web Applications (PWAs), web applications that can be installed on a user’s device and work offline.</p>
<p class="graf graf--p">This article will explore the techniques and technologies used to create offline-capable and reliable web applications.</p>

<h3 class="graf graf--h3">I. Introduction</h3>
<p class="graf graf--p">Today, people rely on web applications for various tasks, from ordering food to managing finances.</p>
<p class="graf graf--p">As such, these applications must be available to users even when they don’t have an internet connection. Additionally, users expect web applications to be fast, responsive, and available at all times.</p>
<p class="graf graf--p">PWAs are web applications that can be installed on a user’s device and work offline, providing an experience similar to that of a native mobile app.</p>

<h3 class="graf graf--h3">II. Offline Capability</h3>
<p class="graf graf--p">One of the key features of PWAs is their ability to work offline. This is accomplished by caching static assets (such as HTML, CSS, and JavaScript files) and data on the user’s device. There are several ways to store this information, including LocalStorage and IndexedDB.</p>
<p class="graf graf--p">LocalStorage is a simple key-value store that can store small amounts of data, such as user preferences or authentication tokens. It’s easy to use and well-suited for small amounts of data, but it has a limited capacity and can’t store larger data sets.</p>
<p class="graf graf--p">IndexedDB, on the other hand, is a more powerful data store that allows storing large amounts of structured data. It uses an object-oriented data model, making it more complex than LocalStorage, but also more powerful.</p>
<p class="graf graf--p">Service workers, a scriptable network proxy, allow you to control how the browser handles network requests, including serving assets and data from the cache when the network is unavailable.</p>
<p class="graf graf--p">It runs separately from the web application and can operate on a separate thread, allowing for more efficient management of assets and data.</p>

<h3 class="graf graf--h3">III. Reliability</h3>
<p class="graf graf--p">PWAs provide a reliable offline experience by using service workers to control how network requests are handled. Service workers can intercept network requests and check for a cached response before requesting data from the network.</p>
<p class="graf graf--p">Additionally, they can queue requests when the network is unavailable and send them when the connection is restored. This allows the web application to continue functioning even when the user’s device is offline.</p>
<p class="graf graf--p">Push notifications and background sync are other features that can be used to improve the reliability of a PWA. Push notifications allow the application to notify the user of new content or updates even when the app is not open. In contrast, background sync allows the app to perform tasks like uploading data when the device is connected to the internet.</p>

<h3 class="graf graf--h3">IV. PWA implementation</h3>
<p class="graf graf--p">Various libraries and frameworks are available to help with the development of PWAs.</p>
<p class="graf graf--p">One popular choice is Workbox, a set of libraries and Node modules created by Google that makes it easier to add service workers and other PWA features to your web application.</p>
<p class="graf graf--p">When designing and implementing a PWA, it’s essential to keep in mind best practices such as designing for offline functionality, ensuring fast load times, and using appropriate storage options. It’s also essential to test the PWA on different devices and network conditions to ensure it works correctly.</p>
<p class="graf graf--p"><strong class="markup--strong markup--p-strong">Examples of successful PWAs:</strong></p>

<ul class="postList">
 	<li class="graf graf--li"><strong class="markup--strong markup--li-strong">Twitter Lite</strong> is a lightweight version of the Twitter app that uses a PWA to provide an offline-capable and fast user experience.</li>
 	<li class="graf graf--li"><strong class="markup--strong markup--li-strong">Alibaba</strong> is a popular e-commerce platform that uses a PWA to provide shoppers a fast and reliable offline experience.</li>
 	<li class="graf graf--li"><strong class="markup--strong markup--li-strong">Spotify</strong> is a music streaming app that uses a PWA to provide an offline listening experience for users.</li>
 	<li class="graf graf--li"><strong class="markup--strong markup--li-strong">Forbes</strong> is a business and financial news website that uses a PWA to provide readers a fast and offline-capable experience.</li>
 	<li class="graf graf--li"><strong class="markup--strong markup--li-strong">Trivago,</strong> a hotel and travel price comparison website, the PWA offers an improved user experience and faster load time.</li>
 	<li class="graf graf--li"><strong class="markup--strong markup--li-strong">Google Maps Go</strong> is a lightweight app that uses a PWA to provide an offline-capable and fast user experience.</li>
</ul>
<p class="graf graf--p">These are only a few examples of the many PWAs available today. Across various industries and use cases, PWAs are becoming more popular and widely adopted by companies to improve user experience and provide the offline capability.</p>
<p class="graf graf--p"><strong class="markup--strong markup--p-strong">Best Practices for Designing and Implementing a PWA:</strong></p>

<ul class="postList">
 	<li class="graf graf--li">Use a Service Worker to cache static assets and handle network requests</li>
 	<li class="graf graf--li">Use a web manifest file to specify the start URL, display mode, and other PWA features</li>
 	<li class="graf graf--li">Use HTTPS to ensure that the PWA is secure and that service workers can be used</li>
 	<li class="graf graf--li">Use responsive design techniques to ensure that the PWA works well on different devices and screen sizes</li>
 	<li class="graf graf--li">Use push notifications and background sync to provide a reliable experience even when the user is offline</li>
 	<li class="graf graf--li">Test the PWA on different devices and network conditions to ensure that it works correctly</li>
 	<li class="graf graf--li">Keep the PWA’s initial load time as short as possible</li>
 	<li class="graf graf--li">Use appropriate storage options: consider using both LocalStorage and IndexedDB</li>
 	<li class="graf graf--li">Optimize the performance using techniques such as code splitting, preloading and pre-caching</li>
 	<li class="graf graf--li">Continuously monitor and measure the performance</li>
</ul>
<p class="graf graf--p">Use case:</p>
<p class="graf graf--p">A weather PWA app that allows users to check the current weather in their location or any other location they search for. The app will cache the weather data and allow the user to access the data even when offline.</p>
<p class="graf graf--p">To implement this PWA, we will use the following technologies:</p>

<ul class="postList">
 	<li class="graf graf--li">HTML and CSS for the app layout and styling</li>
 	<li class="graf graf--li">JavaScript for the app logic and interacting with the API</li>
 	<li class="graf graf--li">Geolocation API for getting the user’s location</li>
 	<li class="graf graf--li">OpenWeatherMap API for getting weather data</li>
 	<li class="graf graf--li">Workbox for caching the weather data and assets</li>
</ul>
<p class="graf graf--p"><strong class="markup--strong markup--p-strong">Here’s an example of how the app’s code might look like:</strong></p>

```html
<!DOCTYPE html>
<html>
<head>
<title>Weather PWA</title>
<link rel="manifest" href="manifest.json">
</head>
<body>
<header>
<h1>Weather PWA</h1>
</header>
<main>
<div id="location"></div>
<div id="weather"></div>
</main>
<footer>
<p>Copyright 2021</p>
</footer>
</body>
</html>
CSS:
body {
font-family: sans-serif;
padding: 0;
margin: 0;
}
header {
background-color: #f1f1f1;
padding: 20px;
text-align: center;
}
main {
padding: 20px;
text-align: center;
}
footer {
background-color: #f1f1f1;
padding: 10px;
text-align: center;
}
```

```javascript

// Get the user's location
navigator.geolocation.getCurrentPosition(getWeather);
function getWeather(position) {
const lat = position.coords.latitude;
const lon = position.coords.longitude;
// Make an API request to OpenWeatherMap
fetch(`https://api.openweathermap.org/data/2.5/weather?lat=${lat}&lon=${lon}&appid=<your-api-key>`)
.then(response => response.json())
.then(data => {
const location = data.name;
const temperature = data.main.temp;
// Display the weather data on the page
const locationElem = document.getElementById('location');
locationElem.innerHTML = `Location: ${location}`;
const weatherElem = document.getElementById('weather');
weatherElem.innerHTML = `Temperature: ${temperature}`;
})
.catch(err => console.log(err));
// Register the service worker
if ('serviceWorker' in navigator) {
navigator.serviceWorker
.register('/serviceWorker.js')
.then(() => console.log('Service worker registered'))
.catch(err => console.log(err));
}
serviceWorker.js

// Import Workbox
importScripts('https://storage.googleapis.com/workbox-cdn/releases/4.3.1/workbox-sw.js');
// Use the precaching module to cache the app's static assets
workbox.precaching.precacheAndRoute([
{url: '/index.html', revision: '1'},
{url: '/styles.css', revision: '1'},
{url: '/script.js', revision: '1'},
]);
// Use the caching module to cache the weather data
workbox.routing.registerRoute(
/^https:\/\/api\.openweathermap\.org/,
new workbox.strategies.StaleWhileRevalidate(),
);
}
```

<li class="graf graf--li">Geolocation API: This API allows web applications to access the user’s location information. In the example above, we used the <strong class="markup--strong markup--li-strong">navigator.geolocation.getCurrentPosition()</strong> method to get the user’s current location and passed that information to the <strong class="markup--strong markup--li-strong">getWeather()</strong> function.</li>
 	<li class="graf graf--li">OpenWeatherMap API: This API is used to get weather data for a specific location. In the example above, we requested the API to get the current weather data for the user’s location. We used the returned data to display the location and temperature on the page.</li>
 	<li class="graf graf--li">Workbox: Workbox is a set of libraries and Node modules created by Google that makes it easy to add service worker features to your web application. In the example above, we used Workbox’s precaching module for caching the app’s static assets and its caching module for caching the weather data. This way, the PWA can access this data even when the user is offline.</li>
</ol>
<p class="graf graf--p">Using these technologies, the example of a PWA capable of obtaining user location, fetching weather data and caching it to provide an offline experience is implemented.</p>
<p class="graf graf--p">Please note that the API key and endpoint URL may differ, and you will have to acquire one from the OpenWeatherMap service and use it in the app.</p>

<h3 class="graf graf--h3">Conclusion</h3>
<p class="graf graf--p">In conclusion, building a Progressive Web Application (PWA) allows web applications to provide an offline-capable and reliable user experience.</p>
<p class="graf graf--p">PWAs can continue functioning even when the user is offline by utilising service workers to cache assets and data. Additionally, by utilizing the Geolocation API and OpenWeatherMap API, the PWA can gather information from the users and provide a personalized experience.</p>
<p class="graf graf--p">Furthermore, by utilizing Workbox, developers can quickly implement service worker features such as offline caching and background sync.</p>

<h3 class="graf graf--h3">Resource</h3>
<ul class="postList">
 	<li class="graf graf--li"><a class="markup--anchor markup--li-anchor" href="https://developers.google.com/codelabs/pwa-training/pwa03--going-offline" target="_blank" rel="noreferrer nofollow noopener noopener" data-href="https://developers.google.com/codelabs/pwa-training/pwa03--going-offline">Google Developers</a></li>
 	<li class="graf graf--li"><a class="markup--anchor markup--li-anchor" href="https://developers.google.com/codelabs/pwa-training/pwa03--going-offline" target="_blank" rel="noreferrer nofollow noopener noopener" data-href="https://developers.google.com/codelabs/pwa-training/pwa03--going-offline">educative</a></li>
</ul>