Hooks can extend, replace, filter data or change the default behavior. Each hook is identified with a unique name, example: `controller:calendar:user:events`
### Listen on hook events
In your `initialize()` method you need to call the method `on()` of the class `Kanboard\Core\Plugin\Hook`:
```php
$this->hook->on('hook_name', $callable);
```
The first argument is the name of the hook and the second is a PHP callable.
- Override subtask time tracking events to display the calendar
- Arguments:
-`$user_id` (integer)
-`$events` (array)
-`$start` (string, ISO-8601 format)
-`$end` (string, ISO-8601 format)
### Merge hooks
"Merge hooks" act in the same way as the function `array_merge`. The hook callback must return an array. This array will be merged with the default one.
Example to add events in the user calendar:
```php
class Plugin extends Base
{
public function initialize()
{
$container = $this->container;
$this->hook->on('controller:calendar:user:events', function($user_id, $start, $end) use ($container) {
$model = new SubtaskForecast($container);
return $model->getCalendarEvents($user_id, $end); // Return new events
Asset hooks can be used to add a new stylesheet easily or a new JavaScript file in the layout. You can use this feature to create a theme and override all Kanboard default styles.
