Technologies Coding Problems Bookmarks Learning Paths

Technologies Coding Problems Bookmarks Learning Paths

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Questions

6 of 6

1Explain what is virtual DOM?

2Explain how virtual DOM works?

3Explain advantages of Virtual DOM?

4Describe the process of reconciliation in React and how it helps in efficiently updating the actual DOM.

5What is the difference between Virtual DOM and Shadow DOM?

6What are portals in ReactJS?

react

State and Props

Class Components

Function Components

Lifecycle functions

Performance Optimisation

06 / 06

What are portals in ReactJS?

Difficulty: 6/10

ReactDOM.createPortal, modal implementation, event handling

Portal is a way to render children into a DOM node that exists outside the DOM hierarchy of the parent component.

The first argument (child) is any renderable React child, such as an element, string, or fragment. The second argument (container) is a DOM element.

Scenario Questions

0-2 years experience

1How would you render a tooltip so it appears above other elements without being clipped by its parent’s overflow:hidden style?
2If you need to mount a modal dialog into a div that lives outside your main app root, which React feature would you use and how would you implement it?
3What happens if you try to create a portal targeting a DOM node that hasn’t been added to the page yet?

2-5 years experience

Follow-up Questions

What are the common pitfalls with event propagation when using portals?
How do you ensure the portal container is properly cleaned up on unmount?
Can you outline a testing approach for a component that renders via a portal?

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What are portals in ReactJS? | Virtual DOM | react Interview Questions | NextRound.in

1We have a modal that sometimes fails to close when clicking outside while it’s rendered via a portal. How would you debug and fix it?
2When adding a portal for a dropdown menu, what trade‑offs do you consider regarding event bubbling and focus management?
3Explain why a portal might break server‑side rendering and how you would guard against that scenario.

5-8 years experience

1Our app renders many portals for tooltips and popovers. How would you design a reusable portal system that minimizes re‑renders and avoids memory leaks?
2Discuss the performance implications of mounting a large number of portals on a high‑traffic page and how you would mitigate any issues.
3How would you handle accessibility (ARIA) and keyboard navigation for components rendered via portals across different browsers?

8+ years experience

1We are migrating a legacy codebase that uses jQuery modals to React portals. What architectural steps would you take to ensure a smooth transition and long‑term maintainability?
2Across multiple teams, some portals render into a shared DOM node while others use separate roots. How would you establish a consistent strategy and enforce it?
3If you need to support server‑side rendering for a component that conditionally uses a portal, how would you design the rendering pipeline to avoid hydration mismatches?