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JavaScript Hello World Sample - PWA

PWA is short for Progressive Web Apps which stand for web applications that have been designed to behave like platform-specific (native) applications. Check out the following on how to implement Dynamsoft Barcode Reader JavaScript SDK (hereafter called “the library”) into a PWA application.

Official Sample

Preparation

We will try to turn our most basic hello world sample into a PWA.

First, create a file with the name “helloworld-pwa.html” and fill it with the following code:

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width,initial-scale=1.0">
    <title>Dynamsoft Barcode Reader PWA Sample - Hello World (Decoding via Camera)</title>
</head>

<body>
    <h1 style="font-size: 1.5em;">Hello World for PWA</h1>
    Loading...
    <script src="https://cdn.jsdelivr.net/npm/dynamsoft-javascript-barcode@9.6.33/dist/dbr.js"></script>
    <script>
        Dynamsoft.DBR.BarcodeReader.license = 'DLS2eyJvcmdhbml6YXRpb25JRCI6IjIwMDAwMSJ9';
        (async function() {
            try {
                const scanner = await Dynamsoft.DBR.BarcodeScanner.createInstance();
                scanner.onFrameRead = results => {
                    console.log("Barcodes on one frame:");
                    for (let result of results) {
                        const format = result.barcodeFormatString;
                        console.log(format + ": " + result.barcodeText);
                    }
                };
                scanner.onUniqueRead = (txt, result) => {
                    alert(txt);
                    console.log("Unique Code Found: ", result);
                }
                await scanner.show();
            } catch (ex) {
                let errMsg = ex.message||ex;
                console.error(errMsg);
                alert(errMsg);
            }
        })();
        
        if ('serviceWorker' in navigator) {
            navigator.serviceWorker.register('./service-worker.js');
        };
    </script>
</body>

</html>

Next, set up a secure environment (HTTPs) to run the page “helloworld-pwa.html”. This is required because PWAs only run in secure environments.

In our case, we use IIS to set up a secure site at “https://localhost” and the page is put at the root so that it can be accessed at “https://localhost/helloworld-pwa.html”.

Make the app progressive

Register a service worker for offline support

As the basis for PWAs, Service Workers are a virtual proxy between the browser and the network. A service worker can serve content offline, handle notifications and perform heavy calculations, etc. all on a separate thread.

To use a service worker, we first need to register it. In the helloworld-pwa.html file, add the following at the end of the script:

if ('serviceWorker' in navigator) {
    navigator.serviceWorker.register('./service-worker.js');
};

Create the service-worker.js file with the following content:

// Files to cache
const cacheName = 'helloworld-pwa';
const appShellFiles = [
    './helloworld-pwa.html',
];

// Installing Service Worker
self.addEventListener('install', (e) => {
    console.log('[Service Worker] Install');
    e.waitUntil((async () => {
        const cache = await caches.open(cacheName);
        console.log('[Service Worker] Caching all: app shell and content');
        await cache.addAll(appShellFiles);
    })());
});

self.addEventListener('fetch', (e) => {
    e.respondWith((async () => {
        const r = await caches.match(e.request);
        console.log(`[Service Worker] Fetching resource: ${e.request.url}`);
        if (r) { return r; }
        const response = await fetch(e.request);
        const cache = await caches.open(cacheName);
        console.log(`[Service Worker] Caching new resource: ${e.request.url}`);
        if (e.request.method !== "POST")
            cache.put(e.request, response.clone());
        return response;
    })());
});

With the above code, the application can now work offline because the service worker will cache the page helloworld-pwa.html and its related resources.

For more information, refer to Making PWAs work offline with Service workers.

NOTE

Since the files are being cached, changes we make in later steps may not be reflected. Therefore, don’t forget to clear the cache after a change is made. To do so, you can run the following in the browser console.

const cacheName = 'helloworld-pwa';
const cache = await caches.delete(cacheName);

Use a web manifest file to make the application installable

A web manifest file contains a list of information about a website in a JSON format. This information is used to present the web app correctly for installation on a device.

In our example, we first create a file “helloworld-pwa.webmanifest” with the following content:

{
    "name": "Dynamsoft Barcode Reader Progressive Web App",
    "short_name": "DBR-PWA",
    "description": "Progressive Web App that reads barcodes from a video input with Dynamsoft Barcode Reader.",
    "start_url": "./helloworld-pwa.html",
    "scope": ".",
    "display": "standalone",
    "theme_color": "#B12A34",
    "background_color": "#B12A34",
    "icons": [
        {
          "src": "./dynamsoft-512x512.png",
          "sizes": "512x512",
          "type": "image/png"
        },
        {
          "src": "./dynamsoft-192x192.png",
          "sizes": "192x192",
          "type": "image/png"
        }
    ]
}

The icon files can be found in the github repository.

Then we include the file in the <head> block of the helloworld-pwa.html file:

<link rel="manifest" href="helloworld-pwa.webmanifest">

For compatibility on safari, we need add some meta in <head>:

<meta name="theme-color" content="#B12A34">
<meta name="mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-title" content="sample for ios">
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="default">
<link rel="apple-touch-icon" sizes="192x192" href="./dynamsoft-192x192.png" />
<link rel="apple-touch-icon" sizes="512x512" href="./dynamsoft-512x512.png" />

Now, if you open the application again in your browser, you will notice an install icon appear on the right side of the address bar. When you click on it, a pop-up will appear asking if you want to install the app.

Once installed, you can use it like a native app.

For offline use, you need to cache more files.

service-worker.js

const dbrVersion = "9.6.11";
const dbrCdn = `https://cdn.jsdelivr.net/npm/dynamsoft-javascript-barcode@${dbrVersion}/dist/`;

const appShellFiles = [
    './helloworld-pwa.html',
    './dynamsoft-192x192.png',
    './dynamsoft-512x512.png',
    './helloworld-pwa.json',
    `${dbrCdn}dbr.js`,
    `${dbrCdn}dbr-${dbrVersion}.full.wasm`,
    `${dbrCdn}dbr-${dbrVersion}.full.wasm.js`,
    `${dbrCdn}dbr-${dbrVersion}.browser.worker.js`,
];

Summary

In this article we took a look at how you can turn a simple barcode reading page into a PWA that is installable, re-engageable and capable of working offline. To learn more about Progressive web apps, you can click here.

This page is compatible for:

Version 7.5.0

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