QReact · Interview preparation
When is useReducer better than useState?
A reducer is useful when state transitions involve several related fields or multiple distinct actions.
The idea to remember.
A reducer is useful when state transitions involve several related fields or multiple distinct actions. It expresses each transition in one predictable function rather than scattering update logic across handlers.
01Learn by doing
From first example to real project.
Start with the smallest working idea, examine a more detailed example, then look at a real application pattern. Adapt dependencies, error handling and data models to your project.
Basic: pass content through children
01 / BEGINNERCompose a reusable panel without hardcoding its content.
function Panel({ title, children }) {
return <section><h2>{title}</h2>{children}</section>;
}Intermediate: share state with context
02 / INTERMEDIATEPut truly shared values in context, not every temporary input.
const ThemeContext = React.createContext('light');
function ThemeLabel() {
const theme = React.useContext(ThemeContext);
return <span>Theme: {theme}</span>;
}Real scenario: reducer for complex UI
03 / REAL SCENARIOGroup related updates in a reducer for a multi-step workflow.
function reducer(state, action) {
if (action.type === 'NEXT') return { ...state, step: state.step + 1 };
if (action.type === 'BACK') return { ...state, step: Math.max(0, state.step - 1) };
return state;
}
const [wizard, dispatch] = React.useReducer(reducer, { step: 0 });02Check your understanding
Try it in your own words.
Explain when is useReducer better than useState without looking at the code. Then modify the intermediate example, describe one trade-off and identify when the real-world pattern fits.
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