> For the complete documentation index, see [llms.txt](https://api.beacon.li/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://api.beacon.li/callbacks-in-beacon/add-callbacks-in-beacon.md).

# Add Callbacks in Beacon

In the `@beacon.li/bar` package, you can add callbacks to execute custom logic whenever a specific event occur. These callbacks allow you to extend and customize the behavior of BeaconBar.

#### Adding a Callback

To add a callback, you can use the `Beacon.addCallback` method. This method takes two parameters:

1. `key` (string): The key of the callback. This key should be unique to identify the callback.
2. `callback` (function): The callback function to be executed when the event occurs. The callback function signature should be `(userId, metaData) => {}`, where `userId` and `metaData` are optional parameters.

Here's how to use it:

```
import { Beacon } from '@beacon.li/bar';
Beacon.addCallback('your_callback_key', (userId, metaData) => {
    // Your custom logic here
});
```

In the example above, we've added a callback with the key `'your_callback_key'`. This callback will execute your custom logic when triggered.

#### Parameters

* `key` (string): A unique identifier for the callback. Adding a callback with the same key as an existing one will replace the old callback.
* `callback` (function): The callback function to execute. It receives two optional parameters:
  * `userId` (string, default: `beacon-anonymous`): The unique identifier passed during `loadUser`.
  * `metaData` (object, default: `{}`): The `metaData` object passed during `loadUser`.

#### Replacing Callbacks

It's important to note that adding a callback with the same key as an existing one will replace the old callback. This allows you to update callback logic dynamically when needed.

#### Use Cases

Callbacks can be useful for various scenarios, such as:

* Responding to specific user interactions within BeaconBar.
* Customizing the behavior of beacon based on user data or actions.
* Integrating with external systems or services when certain events occur.

By following these steps, you can add custom callbacks to enhance the functionality and customization of BeaconBar in your application.