What are reducers in Redux?

beginner

Re-explain

Reducers are pure functions that take the current state and an action, and return a new state. They specify how the application's state changes in response to actions.

const todosReducer = (state = [], action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return [...state, action.payload];
    case 'REMOVE_TODO':
      return state.filter(todo => todo.id !== action.payload.id);
    default:
      return state;
  }
};

Rewriting in plainer words…

This answer doesn't lend itself to a diagram - it reads best . No credits were charged.

The model's verdict: “”

The interactive diagram is below the answer - jump to diagram ↓

This answer is explained by a shared concept diagram - open →

Tailored explanation · switch back to · ·

Point the redraw:

How well did you know this?

AI:

Saved in this browser - sign in to keep your review list.

How should your speech become text?

Listening… your words appear above as you speak - tap Stop when you're done.

Recording · cr - tap Stop & transcribe when you're done.

Transcribing with AI…

Voice:

Keep going - a few more words and AI can grade it.

Interview lens

Likely follow-ups, what you can say, and the weak answers to avoid.

Want a quick review of the fundamentals? See the Redux cheatsheet.

← Back to all Redux questions

Pro · $10/mo

42 of 49 Redux answers are gated.

Full answers, code samples, AI explanations - simpler, deeper, or as an interactive diagram. Cancel anytime.

Full answers + code
AI explain - simpler, deeper, or visualized
1,000 AI credits / month
Cancel anytime

Get Pro → See plans & pricing →