You generally have three choices when it comes to state. You can either use something like an event bus, raise events for others to change their state, move the state to the top and manage all those changes at once, or have something that manages the state of children.

An example would be if you have accordions setup that causes any open accordions to close when a different one is open. If you go with an event bus, each component would setup listeners for something like 'accordion:opened' set their state to close if the opened accordion wasn't theirs. If you move state to the top you'd set all other accordions to closed based off the event and rerender. The last would be an accordion group component that manages all the state for the children, which ultimately is a more localized version of moving state all the way to the top.

Stateless functions just take input and give output without storing anything. This would be accordions with a group that manages the state of the children or by fully moving it all the way to the top, so external functions handle the state. When you use the event bus approach you localize all state within the component and it is no longer a simple given A, you get B.