Tell me about state management: which libraries have you used, and tell me about the Redux architecture.

State management — managing the application's state, especially important in complex SPAs.

Libraries I have used:

• Redux — a classic and popular state manager with a predictable data flow.
• MobX — a reactive approach with automatic change tracking.
• React Context — for simple global state without third-party libraries.

Redux Architecture:

• Store — a single object that holds the entire application state.
• Actions — objects describing an event or intention to change the state.
• Reducers — pure functions that take the current state and an action, returning a new state.
• Dispatch — a method to send actions to the store.
• Subscription (subscribe) — allows components to react to state changes.

Main principles:

• Single source of truth (store).
• State is read-only.
• Changes via pure functions (reducers).

Example reducer:

const initialState = { count: 0 };

function counterReducer(state = initialState, action) {
  switch(action.type) {
    case 'INCREMENT':
      return { count: state.count + 1 };
    case 'DECREMENT':
      return { count: state.count - 1 };
    default:
      return state;
  }
}

Redux helps centralize the logic of state changes, making debugging and scaling applications easier.