HTML, CSS, JavaScript and React interview questions

200 means success so I render the data.

Divs have no meaning, so screen readers and outline tools cannot find nav, headings, or lists.

Em is relative to the parent font-size, so it compounds in nested components.

It turns a JS value into a JSON string for APIs or localStorage.

It stops the browser's default action, like following a link or submitting a form.

Hooks let us reuse stateful logic without HOCs and mixins.

A class can be reused on many elements

Map returns a new array of transformed items and is the React list pattern.

Both download the script without blocking HTML parse.

UseEffect runs after paint for side effects: fetch, subscriptions, and syncing to document title.

The modern answer is flex on the parent with justify-content and align-items set to center, or grid with place-items center.

Flex-grow is how leftover space is shared

I use a grid with two columns on min-width 768 and one column in the base styles.

Z-index is compared only inside the same stacking context.

Fixed is relative to the viewport and stays put even when you scroll the page.

I start with a button that has aria-expanded and aria-controls pointing at the list.

Inside a form, the default type is submit, so a random button can post the form by accident.

Synchronous code runs on the call stack until it is empty.

Microtasks include Promise callbacks and queueMicrotask and they flush completely before the next macrotask.

Objects have an internal prototype link used when a property is missing.