## LoaderStart event

`element.on(event: 'loaderstart', handler: function)`

Triggered when the loader UI is mounted to the DOM and ready to be displayed.

See also: [Elements methods](https://docs.stripe.com/js/custom_checkout/custom_checkout_elements.md) | [Listen to Elements events](https://docs.stripe.com/js/custom_checkout/element_events.md)

- `event`
The name of the event. In this case, `loaderstart`.

- `handler`
`handler(event) => void` is a **callback function** that you provide that will be called when the event is fired. When called it will be passed an event object with the following properties:

- `elementType`
The type of element that emitted this event.

### Example

```title
Handle a Checkout Element loaderstart event
```