What are portals in ReactJS?

0-2 years experience

1. 1How would you render a tooltip so it appears above other elements without being clipped by its parent’s overflow:hidden style?
2. 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?
3. 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

1. 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?
2. 2When adding a portal for a dropdown menu, what trade‑offs do you consider regarding event bubbling and focus management?
3. 3Explain why a portal might break server‑side rendering and how you would guard against that scenario.

5-8 years experience

1. 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?
2. 2Discuss the performance implications of mounting a large number of portals on a high‑traffic page and how you would mitigate any issues.
3. 3How would you handle accessibility (ARIA) and keyboard navigation for components rendered via portals across different browsers?

8+ years experience

1. 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?
2. 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?
3. 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?