Frontend interview guide

Elements communicate purpose: a button performs an action, an anchor navigates, and headings describe document structure. Native semantics improve keyboard and assistive-technology behavior.

Follow-up: Replace a clickable div with a button and explain the keyboard difference.

Reproduce at the failing width, inspect computed styles, find fixed widths or overflow, and check long content. Fix the cause before adding a breakpoint.

Follow-up: What happens when the user zooms to 200%?

Both are block-scoped. const prevents reassignment of the binding, not mutation of the referenced object. Use const when the binding does not need reassignment.

Follow-up: Can a const array receive a new item?

Catch network failures, inspect response.ok for HTTP errors, validate the response shape, and present a retry path. Abort stale requests where appropriate.

Follow-up: Why can a 404 response still resolve the fetch promise?

Calculate filtered results from source data and the filter instead of storing a second independently updated list. This avoids inconsistent copies.

Follow-up: When would memoization be useful, and when is it unnecessary?

Cover matching, no match, mixed case, empty data and clearing the filter. Assert user-visible results rather than implementation details.

Follow-up: How would keyboard-only users operate it?

Untrusted content interpreted as markup or script can execute in the page. Render plain text with textContent; sanitize intentionally allowed HTML with a maintained approach.

Follow-up: Why is client-side input validation alone insufficient?

Verify the behavior and API assumptions, inspect dependencies and security boundaries, add meaningful tests and ensure you can explain the change.

Follow-up: Show a case where a plausible implementation fails.