What are stateless and stateful components?

Q: What are stateless and stateful components?

They are typically written as functions. They are pure functions, meaning they always return the same output for the same input (props). They are primarily used for rendering UI and do not handle logic related to state or lifecycle methods. They are easier to test and maintain because of their simplicity. They are typically written as classes (before React 16.8) or as functional components using hooks (after React 16.8). They can manage state using this.state (in class components) or the useState hook (in functional components). They can handle lifecycle methods (e.g., componentDidMount, componentDidUpdate) or use the useEffect hook in functional components. They are used when the component needs to maintain or update data over time.

Difficulty: 5/10

component design, state management, performance

It has a corresponding element created in the DOM and is connected to that.

Stateless components are components that do not manage their own state. They rely solely on the data passed to them via props.

1
They are typically written as functions.
2
They are pure functions, meaning they always return the same output for the same input (props).
3
They are primarily used for rendering UI and do not handle logic related to state or lifecycle methods.
4
They are easier to test and maintain because of their simplicity.

Stateful components are components that manage their own state. They can hold and update data internally.

1
They are typically written as classes (before React 16.8) or as functional components using hooks (after React 16.8).
2
They can manage state using this.state (in class components) or the useState hook (in functional components).
3
They can handle lifecycle methods (e.g., componentDidMount, componentDidUpdate) or use the useEffect hook in functional components.
4
They are used when the component needs to maintain or update data over time.

Scenario Questions

0-2 years experience

2-5 years experience

1While adding a search filter to a dashboard, the filter component started re‑rendering the entire page on every keystroke. Walk me through how you would diagnose whether the component should be stateless or stateful.

Follow-up Questions