Discuss 'useReducer' hook.

Q: Discuss 'useReducer' hook.

const [state, dispatch] = useReducer(reducer, initialArg, init?) It must be pure, should take the state and action as arguments It should return the next state. State and action can be of any type. initialArg: The value from which the initial state is calculated. It can be a value of any type. How the initial state is calculated from it depends on the next init argument. If it’s not specified, the initial state is set to initialArg. Otherwise, the initial state is set to the result of calling init(initialArg). The current state. During the first render, it’s set to init or initialArg (if there’s no init). The dispatch function lets you update the state to a different value and trigger a re-render.

Difficulty: 6/10

state management, reducer patterns, performance

useReducer is very similar to useState, but it lets you move the state update logic from event handlers into a single function outside of your component.

useReducer is a React Hook that lets you add a reducer to your component state.

reducer: The reducer function specifies how the state gets updated.

1
It must be pure, should take the state and action as arguments
2
It should return the next state. State and action can be of any type.

initialArg: The value from which the initial state is calculated. It can be a value of any type. How the initial state is calculated from it depends on the next init argument.

optional init: The initialiser function that should return the initial state.

1
If it’s not specified, the initial state is set to initialArg.
2
Otherwise, the initial state is set to the result of calling init(initialArg).

useReducer returns an array with exactly two values:

1
The current state. During the first render, it’s set to init or initialArg (if there’s no init).
2
The dispatch function lets you update the state to a different value and trigger a re-render.

Scenario Questions

0-2 years experience

2-5 years experience

1We're building a multi‑field form with validation. Explain how you'd structure the reducer and actions to handle field updates and validation errors.

Follow-up Questions