Action

Actions are used to update the state in a functional way.
They are so called reducers that receive both the current state and some payload and return the new state.

type Action = (previousState: any, ...payload) => any

While it doesn't enforce any restrictions on how to calculate the new state, here are some recommendations:

• Do not mutate the current state, but rather use immutable data structures
• Ensure that all actions are pure functions
• All actions should have a single responsibility

Pure Functions

A pure function should:

• always return the same output for given input
• not manipulate the input
• not cause side effects (e.g. API calls)

Unidirectional Data Flow

Given that the only way to update the state is calling a action, we always have an unidirectional data flow.
Calling actions will automatically update the state and rerender all consuming components to ensure predictable and up-to-date output.