List built in components in react.

1
<Fragment>, alternatively written as <>...</>, lets you group multiple JSX nodes together.
2
<Profiler> lets you measure the rendering performance of a React tree programmatically.
3
<Suspense> lets you display a fallback while the child components are loading.
4
<StrictMode> enables extra development-only checks that help you find bugs early.
5
<DeferredValue> While primarily used as a hook (useDeferredValue), the concept is built into the React engine to help you defer updating a non-urgent part of the UI. This is often used to keep an input field responsive while a heavy list filters in the background.
6
Metadata Components React 19 introduced built-in support for rendering document metadata tags anywhere in your component tree. React will automatically hoist these to the <head> of the HTML document.

Difficulty: 3/10

Topics: core components, React APIs, performance

0-2 years experience

1
How would you use React.Fragment to return multiple sibling elements without adding extra DOM nodes?
2
If you wrap a lazily loaded component with <Suspense>, what does the fallback prop do, and when does it appear?
3
What happens if you pass a non‑standard HTML attribute to a built‑in element like <div>?

2-5 years experience

1
You added a <Suspense> wrapper around a lazy component but the fallback never shows during a slow network request. What could be causing this and how would you fix it?
2
When you enable <StrictMode> in development, certain lifecycle methods run twice. Explain why this happens and how you would adjust your code if needed.
3
You need to measure render performance of a component. Which built‑in component would you use and what steps would you take to interpret its data?

5-8 years experience

1
Your application uses many portals for modals and tooltips, and you start seeing memory leaks after navigating between routes. How would you investigate and resolve portal‑related leaks?
2
The team wants to adopt React.StrictMode globally across a large codebase. What trade‑offs should you consider, and how would you ensure existing components continue to work correctly?
3
You are collecting performance metrics with <Profiler> across multiple pages. How would you design a system to aggregate this data without impacting user experience?

8+ years experience

1
Across several repositories, the organization wants to standardize the use of React.Fragment versus the <> shorthand. What guidelines would you establish and how would you enforce them at scale?
2
Looking ahead to future React releases, how would you plan for potential deprecation or changes to built‑in components like SuspenseList in a legacy codebase?
3
When migrating a large legacy application from class components to functional components, how would you decide which built‑in components to replace with newer APIs (e.g., using Suspense for data fetching) while minimizing risk?