Interview Q&A / React

1. What is the virtual DOM, and how does reconciliation work in React?

   The virtual DOM is React's lightweight description of what the UI should look like, made of plain JavaScript objects. On each update React compares the new description with the previous one (reconciliation) and changes only the parts of the real DOM that differ.

   BeginnerIn-depth4 min read
2. Why do keys matter when rendering lists in React?

   Keys tell React which list item is which between renders, so it can keep the right state with the right item when the list changes order, grows or shrinks.

   BeginnerIn-depth2 min read
3. What causes a React component to re-render?

   A component re-renders when its own state changes, when its parent re-renders, or when a context it reads changes. Changing a prop value does not itself trigger it; the parent re-rendering does. Plain variables and refs never cause a render.

   BeginnerQuick answer1 min read
4. What does React.StrictMode do?

   StrictMode is a development-only wrapper that helps find bugs. It renders components twice, re-runs effects once after mount and warns about deprecated APIs. It has no effect and no cost in production builds.

   BeginnerQuick answer1 min read