React Quiz — 7 Free Questions

Question 1

What is the "virtual DOM" in React, and what is its main purpose?

Question 2

What is the purpose of the "useDeferredValue" hook in React's concurrent rendering model?

Question 3

What is the purpose of passing a function, rather than a plain value, as the initial argument to useState, e.g. useState(() => expensiveInit())?

Question 4

What must a React functional component return?

Question 5

What does React's Strict Mode () do during development?

Question 6

What is the purpose of the "aria-live" attribute sometimes applied to a dynamically updating region of a React component's rendered output?

Question 7

What is the purpose of passing a function, rather than a plain new value, to a useState updater, e.g. setCount(prev => prev + 1)?

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About React

React came out of Facebook in 2013, built originally by engineer Jordan Walke to solve a very specific internal problem: keeping Facebook's News Feed fast and predictable to update as the product got more complex. Its early design choice to mix HTML-like markup directly into JavaScript code, known as JSX, struck a lot of developers as strange or even backwards at first, going against years of accepted wisdom about separating markup from logic.

Facebook kept using React internally at massive scale well before most of the outside world trusted it, running it across News Feed and later all of Instagram, which gave the library a level of real-world battle-testing that helped win over skeptical developers once it was released publicly.

Rather than release another full framework, Facebook released a deliberately focused library for building UI out of small, reusable components, and let the surrounding ecosystem fill in the gaps around it. That "just the UI layer" philosophy meant developers could pair React with whatever routing, state management, or backend approach fit their specific project, and frameworks like Next.js later grew up specifically to give React a fuller, more opinionated structure for teams that wanted one.

Under the hood, React introduced the idea of a virtual DOM, a lightweight in-memory representation of the page that React compares against the previous version to figure out the smallest possible set of real changes needed, rather than redrawing everything from scratch on every update. That diffing approach became one of the most influential ideas in modern frontend development.

React changed again significantly in 2018 with the introduction of Hooks, which let developers use state and other React features inside simple function components instead of the more verbose class-based components the library originally required, and the ecosystem largely shifted to the new style within just a couple of years.

By most developer surveys, React remains the most widely used frontend library in the world today, and its component-based way of thinking has influenced nearly every UI framework that came after it, including several built specifically to compete directly against it.

React's influence extends well beyond the browser too. React Native, released in 2015, lets developers use the same component-based approach and much of the same knowledge to build genuinely native mobile apps for iOS and Android, rather than writing two completely separate native codebases from scratch, and it's been used for major apps at companies including Discord and Shopify.

More recent versions of React have also introduced concurrent rendering features and Suspense, which let applications handle loading states and data fetching more gracefully, rendering parts of a page as data becomes available instead of blocking the entire interface until everything is ready, a shift that's steadily changing how experienced React developers structure their applications.

React's own documentation and official tutorials have also evolved significantly over the years, shifting from a fairly technical, engineer-focused writing style in its earliest days to a much friendlier, example-driven approach today, a change the React team has explicitly credited with lowering the barrier to entry for developers who might otherwise have been intimidated by the library's early reputation for complexity.