> For the complete documentation index, see [llms.txt](https://pwa.spomky-labs.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://pwa.spomky-labs.com/symfony-ux/sync-broadcast.md).

# Sync Broadcast

The Sync Broadcast controller (`backgroundsync-queue`) monitors background sync queue status using the BroadcastChannel API. It allows your application to display real-time information about pending sync operations and trigger replays.

## Installation

Enable the controller in your `assets/controllers.json`:

{% code title="assets/controllers.json" lineNumbers="true" %}

```json
{
    "controllers": {
        "@spomky-labs/pwa-bundle": {
            "backgroundsync-queue": {
                "enabled": true
            }
        }
    }
}
```

{% endcode %}

## Usage

{% code title="templates/components/sync-status.html.twig" lineNumbers="true" %}

```twig
<div {{ stimulus_controller('pwa/backgroundsync-queue', {
    channel: 'form-sync'
}) }}
    {{ stimulus_action('pwa/backgroundsync-queue', 'replay', 'click') }}
>
    <span {{ stimulus_target('pwa/backgroundsync-queue', 'output') }}>
        Checking sync status...
    </span>
    <button type="button">Retry pending items</button>
</div>
```

{% endcode %}

## Parameters

| Parameter | Type   | Required | Description                                                                                                             |
| --------- | ------ | -------- | ----------------------------------------------------------------------------------------------------------------------- |
| `channel` | String | Yes      | The BroadcastChannel name to listen on. Must match the `broadcast_channel` configured in your background sync strategy. |

## Actions

| Action   | Description                                                                      |
| -------- | -------------------------------------------------------------------------------- |
| `replay` | Requests a replay/resync of all pending operations in the background sync queue. |

## Targets

| Target   | Description                                  |
| -------- | -------------------------------------------- |
| `output` | Element to display queue status information. |

## Events

| Event    | Detail                          | Description                                             |
| -------- | ------------------------------- | ------------------------------------------------------- |
| `error`  | `{ reason }`                    | BroadcastChannel initialization failed.                 |
| `status` | Status data from service worker | Status message received from the background sync queue. |

## How It Works

1. The controller opens a `BroadcastChannel` with the specified name
2. It requests the current sync queue status
3. When the service worker processes queued requests, it broadcasts status updates
4. The controller dispatches `status` events that you can listen for to update the UI
5. The `replay` action tells the service worker to retry all pending requests

## Example: Showing Pending Request Count

{% code title="templates/components/sync-indicator.html.twig" lineNumbers="true" %}

```twig
<div {{ stimulus_controller('pwa/backgroundsync-queue', {
    channel: 'form-sync'
}) }}
    data-action="pwa--backgroundsync-queue:status->updateStatus"
>
    <span class="badge" data-sync-count></span>
    <button {{ stimulus_action('pwa/backgroundsync-queue', 'replay', 'click') }}>
        Sync now
    </button>
</div>

<script>
function updateStatus(event) {
    const badge = document.querySelector('[data-sync-count]');
    badge.textContent = event.detail.pendingCount ?? '0';
}
</script>
```

{% endcode %}

## Related Configuration

This controller works with the [Background Sync](/the-service-worker/workbox/background-sync.md) service worker feature. Make sure the `broadcast_channel` name in your service worker configuration matches the `channel` parameter:

{% code title="config/packages/pwa.yaml" lineNumbers="true" %}

```yaml
pwa:
    serviceworker:
        workbox:
            background_sync:
                - queue_name: 'api-queue'
                  match_callback: 'regex: /\/api\//'
                  method: 'POST'
                  broadcast_channel: 'form-sync'  # Must match controller's channel param
```

{% endcode %}


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