HTML, CSS, JavaScript and React interview questions

The UI dispatches an action object.

A reducer is a function of previous state and action that returns the next state.

Classic Redux needed hand-written action types, switch statements, and spread copies.

I pick interface for object shapes that might be extended or merged in declaration files.

I define a Props interface and annotate the function parameter.

Any turns off checking, so I can access any property and hide bugs.

I model idle, loading, success with data, and error with a message as a discriminated union.

I preload or prioritize the hero image, set explicit dimensions, and avoid lazy-loading that above-the-fold asset.

Media without reserved space, webfonts swapping late, and inserting UI above existing content.

React.lazy plus dynamic import creates a separate chunk loaded when the component first renders.

Bundlers drop unused ES module exports when they can prove they are unused.

I render the form, find fields by label text, type with userEvent, and click the submit button by role.

Classes change during restyles even when the user experience did not.

Aria-label is a string on the element itself.

Native input type checkbox is best.

If you assign a string that contains a script or an onerror handler from the user, the browser will execute it.

HttpOnly stops document.cookie from reading the session, which reduces XSS token theft.

GetStaticProps builds HTML at build time, great for marketing pages.

The HTML from the server does not equal what React renders on the client for the first pass.

They catch errors during render, lifecycle, and constructors of children via componentDidCatch.