HTML, CSS, JavaScript and React interview questions

ARIA attributes tell assistive tech the role, name, and state of custom widgets when native HTML is not enough.

Many users cannot use a mouse, including power users and people with motor disabilities.

Cross-site scripting is when attacker HTML or JavaScript runs in your users' browsers, usually through unsanitized output.

Cross-site request forgery tricks the browser into sending the user's cookies to your API from another site.

Largest Contentful Paint is when the biggest above-the-fold image or text block appears.

Cumulative Layout Shift measures how much the page jumps while loading.

Code splitting breaks the JS bundle so the first paint only downloads the route the user opened.

Jest is a JavaScript test runner with assertions, mocks, and a watch mode.

RTL tests the component the way a user would: find by role or label, click, type, and assert on the screen.

Next.js is a React framework with routing, bundling, and ways to render on the server.

CSR means the server sends JS and the browser builds HTML after download.

Hydration is React attaching to server-rendered HTML instead of throwing it away and painting from scratch.

An error boundary is a class component that catches render errors in its children and shows a fallback UI.

Fetch sends an HTTP request and returns a Promise for the Response.

Display none removes the element from layout so it takes no space.

They apply CSS only when the viewport or device matches a condition, usually min-width.

GET puts fields in the URL and is for safe reads like search.

Falsy values are false, 0, empty string, null, undefined, and NaN.

Spread copies enumerable properties into a new object or array, which we use to update state immutably.

When two siblings need the same data, I move that state to the closest common parent and pass it down as props.