## Change event

`checkout.on(event: 'change', handler: function)`

The change event is triggered when [Checkout Session](https://docs.stripe.com/js/custom_checkout/session_object.md)
data changes, such as when the customer changes their shipping
address.  The event payload is always a [Checkout Session](https://docs.stripe.com/js/custom_checkout/session_object.md)
object.

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

- `handler`
  `handler(session) => void` is a **callback function** that
you provide that will be called when the event is fired. When called
it will be passed a [Checkout Session](https://docs.stripe.com/js/custom_checkout/session_object.md) object.

### Example

```title
Listen to change events
```