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The App Badge API allows installed web apps to set an application-wide badge,
shown in an operating-system-specific place associated with the application
(such as the shelf or home screen).

Badges tend to be more user-friendly than notifications and can be updated with
a much higher frequency since they don’t interrupt the user. And, because they
don’t interrupt the user, they don’t need the user’s permission.

Keep in mind that to display the Badge count, Your PWA application should be installed on your Device.

Possible use cases

Examples of sites that may use this Library includes:

• Chat, email, and social apps, to signal that new messages have arrived, or to
  show the number of unread items.
• Productivity apps, to signal that a long-running background task (such as
  rendering an image or video) has completed.
• Games, to signal that a player action is required (e.g., in Chess, when it is
  the player’s turn).

Usage

npm install --save pwa-badge

The Badge API consists of five methods:

• isSupported() Check if the User’s browser supports the Feature,
  and returns a boolean value that represents the Status of supporting.
• syncSetBadge(unreadCount) Removes app’s badge Synchronously. If a value
  is provided, set the badge to the provided value otherwise, display a plain
  white dot (or other flag as appropriate to the platform). Setting number to 0
  is the same as calling syncClearBadge() or asyncClearBadge().
• syncClearBadge() Removes app’s badge Synchronously.
• asyncSetBadge(unreadCount) This API is the same as syncSetBadge() but
  returns an empty Promise for error handling.
• asyncClearBadge() Removes app’s badge Asynchronously and returns an
  empty Promise for error handling.

Check Browser supports the Badge API

TL;DR isSupported() method function is an util for informing your users that
this feature supports by their Browser or OS and the pwa-badge library
set and clear the Badge count safely, and you can avoid using
isSupported() before calling the set or clear methods.

import PWABadge from 'pwa-badge';

// Create an Instance
const badge = new PWABadge();

if (badge.isSupported()) {
  // Hoora!, Supports the Badge feature
} else {
  // Does not supports
}

Sync Set and Clear Badge

import PWABadge from 'pwa-badge';

// Create an Instance
const badge = new PWABadge();

// Set Badge unreadCount
badge.syncSetBadge(1);

// Clear Badge unreadCount
badge.syncClearBadge();

Result by calling syncSetBadge:

Async Set and Clear Badge

asyncSetBadge() and asyncClearBadge() return empty promises you can
use for error handling.

import PWABadge from 'pwa-badge';

// Create an Instance
const badge = new PWABadge();

// Set Badge unreadCount
badge
  .asyncSetBadge(1)
  .then(() => {
    // Badge count has shown as well
  })
  .catch((e) => {
    // The Browser not supporting the Badge feature or something went wrong
  });

// Clear Badge unreadCount
badge
  .asyncClearBadge()
  .then(() => {
    // Badge count has disappeared
  })
  .catch((e) => {
    // The Browser not supporting the Badge feature or something went wrong
  });

The App Badge API works on Windows, and macOS, in Chrome 81 or
later. It has also been confirmed to work on Edge 84 or later. Support for
Chrome OS is in development and will be available in a future release of
Chrome. On Android, the Badge API is not supported. Instead, Android
automatically shows a badge on app icon for the installed web app when there is
an unread notification, just as for Android apps.

Some user agents may take a number like 4000 and rewrite it as 99+. If you
saturate the badge yourself (for example by setting it to 99) then the +
won’t appear. No matter the actual number, just call syncSetBadge() or
asyncSetBadge() and let the user agent deal with displaying it accordingly.

While the App Badge API in Chrome requires an installed app as I wrote
before, you shouldn’t make calls to the Badge API dependent on the
installation state. Just call the API when it exists and installed on a
device, as other browsers may show the badge in other places. If it works, it
works. If not, it simply doesn’t.