Technologies Coding Problems Bookmarks Learning Paths

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What is reconciliation in React? | Reconciliation | react Interview Questions | NextRound.in

Questions

1 of 13

1What is reconciliation in React?

2What is react fibre?

3What is fibre in react fiber?

4Discuss fibre lifecycle.

5Discuss stack reconciler.

6What is concurrent rendering in react?

7How does React Fiber improve the rendering performance?

8What is the purpose of the `dangerouslySetInnerHTML` attribute in React?

9When rendering a list what is a key and what is its purpose?

10What are low and high-priority updates?

11What is work in progress tree in react fibre?

12Is React Fiber backward compatible with previous versions of React?

13How does React Fiber handle errors?

react

State and Props

Class Components

Function Components

Lifecycle functions

Performance Optimisation

01 / 13

What is reconciliation in React?

Difficulty: 5/10

virtual DOM, diffing algorithm, key management

1
Reconciliation in React refers to the process by which React updates the user interface to match the most recent state and props of a component.
2
it's the mechanism that React uses to determine `what changes need to be made to the DOM in response to changes in the application state or props.

Scenario Questions

0-2 years experience

1If you add a new item to a list rendered with map, how does React decide which DOM nodes to update?
2What happens under the hood when you change a component's state that triggers a re‑render?
3Suppose two sibling components are rendered with the same key—what will React's reconciliation do?

Follow-up Questions

Can you give a concrete example of how changing a key affects the diffing?
What tools or techniques would you use to measure reconciliation overhead?
When would you choose React.memo over useCallback to help reconciliation?

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2-5 years experience

1You notice a list component re‑renders all items when only one changes. How would you investigate if the reconciliation process is the cause?
2During a feature rollout a component sometimes fails to update after its props change. How would you debug whether the diffing algorithm is misbehaving?
3Explain the trade‑offs of using an array index as a key versus a stable unique id in terms of reconciliation performance.

5-8 years experience

1Design a large data‑table component that can handle thousands of rows efficiently. How would you leverage React's reconciliation to minimize DOM work?
2When integrating a third‑party library that mutates the DOM directly, what issues can arise with React's reconciliation, and how would you mitigate them?
3If you need to force a component subtree to skip reconciliation, what approaches can you take and what are the performance implications?

8+ years experience

1Your team is migrating a legacy codebase to React. How would you plan the rollout to ensure that key mismatches or other reconciliation bugs don’t cause regressions across many modules?
2At a company‑wide level you need guidelines for key usage and component memoization to optimize reconciliation. What policies would you propose and how would you enforce them?
3Consider a micro‑frontend architecture where multiple React apps share a page. How does reconciliation interact across app boundaries, and what architectural decisions help avoid conflicts?