---
sidebar_position: 4
---

# Scanner service

The scanner service provides an implementation for barcode and QR code scanning. It follows a subscription pattern where the platform can start/stop scanning and listen for scanned codes.

## Registration

```javascript
export default async context => {
    const listeners = [];

    context.service.addService({
        type: 'scannerService',
        start: async () => {
            // Initialize your scanner hardware
        },
        stop: async () => {
            // Release scanner resources
        },
        onCodeScanned: callback => {
            listeners.push(callback);
            // Return a cleanup function to unsubscribe
            return () => {
                listeners.splice(listeners.indexOf(callback), 1);
            };
        },
    });
};
```

## Methods

### `start()`

Called when the platform wants to activate the scanner. Use this to initialize your scanner hardware or begin listening for scan input.

### `stop()`

Called when the platform wants to deactivate the scanner. Use this to release resources or stop listening for scan input.

### `onCodeScanned(callback)`

Registers a listener that should be called whenever a code is scanned. The callback receives an object with a `code` property containing the scanned value.

Returns a cleanup function that removes the listener when called.

## Dispatching scanned codes

When your scanner hardware detects a code, notify all registered listeners:

```javascript
function onScanDetected(code) {
    for (const listener of listeners) {
        listener({ code });
    }
}
```