Bootstrap provides a specific (somehow limited) plugin to handle modals:

https://getbootstrap.com/docs/4.0/components/modal/

You can ask for a larger or smaller dialog specifing either 'modal-lg' or 'modal-sm' class.

The pluging fires some specific events during the modal life cycle:

https://getbootstrap.com/docs/4.0/components/modal/#events

Code sample

Open Modal Open Large Modal Open Small Modal