Portals and Rendering Control Quiz

Question 1

What does createPortal do?

Accepted Answer

Renders children into a different DOM node while keeping them in the React tree

Answer

Moves a component to a different position in the React tree

Answer

Loads a component lazily

Answer

Creates a new React root

Question 2

Where does a click inside a portal bubble to?

Accepted Answer

Up the React tree, so React parents receive it

Answer

Only to the DOM node it was rendered into

Answer

Nowhere, portals stop propagation

Answer

Directly to document only

Question 3

Which CSS problem does a portal solve?

Accepted Answer

An ancestor's overflow, transform or stacking context clipping or trapping a popup

Answer

Slow style recalculation

Answer

Specificity conflicts

Answer

Unused CSS

Question 4

What does a portal NOT give you for a modal?

Accepted Answer

Focus management, Escape handling and scroll locking

Answer

Escape from ancestor overflow

Answer

The ability to render into document.body

Answer

Access to context

Question 5

Why does Strict Mode render components twice in development?

Accepted Answer

To reveal components that are impure - that change something outside themselves while rendering

Answer

To measure performance

Answer

To warm the cache

Answer

To test error boundaries

Question 6

Your effect runs twice in development. What is the correct response?

Accepted Answer

Add cleanup so the effect can be safely set up and torn down repeatedly

Answer

Disable Strict Mode

Answer

Add a ref guard so it only runs once

Answer

Move the code into the render body

Question 7

What is useInsertionEffect for?

Accepted Answer

Injecting style rules before layout is calculated, for CSS-in-JS libraries

Answer

Inserting elements into the DOM

Answer

Inserting items into a list

Answer

Running effects before state updates

Question 8

When would you use flushSync?

Accepted Answer

When you must read the updated DOM immediately after a state change

Answer

To batch several updates together

Answer

To make rendering concurrent

Answer

To delay an update