Given an array of { id, name } objects, return a Map keyed by id with the object as the value. I am watching for: do they reach for the right tool, do they handle duplicate ids honestly, and can they tell me the runtime?

Quick check

Quick check: indexById([{ id: 'a', name: 'Alice' }, { id: 'b', name: 'Bob' }]) returns Map { 'a' => { id: 'a', name: 'Alice' }, 'b' => { id: 'b', name: 'Bob' } }. On duplicates, indexById([{ id: 'a', name: 'A1' }, { id: 'a', name: 'A2' }]) returns Map { 'a' => { id: 'a', name: 'A2' } } under last-write-wins. The candidate I want flags that convention out loud.

Implement debounce(fn, ms) such that calling the returned function repeatedly only fires fn once, ms after the last call. I am watching for: do they preserve this and arguments, do they handle a cancel, and do they know the difference between this and throttle.

Quick check

const d = debounce(console.log, 200);
d(1); d(2); d(3); // all within 200ms -> logs 3, once, 200ms after the last call
d.cancel();        // before the timer fires -> nothing is logged

Read this fetch wrapper. The candidate spots await response.json() is called on a response that may be a 500 with an HTML body. Walk me through how you would change the function to make that case actually fail loudly.

Quick check

Quick check: api('/users') on a 500 response with HTML body throws ApiError with .status === 500 and .body containing a snippet of the HTML, instead of crashing on JSON.parse. On a 204 No Content the helper returns null because the empty body is detected before parsing.

A user list page fetches users on mount and shows a spinner. The candidate is asked to add a search box that filters as the user types. I am watching for: do they re-fetch on every keystroke, do they debounce, do they understand AbortController?

Quick check

// User types 'al' then 'alice' within 50ms
// -> single fetch for 'alice' fires 200ms after the last keystroke (debounce collapses the rapid keys)
// If a slow 'al' response was already in flight when 'alice' fires:
// -> the 'al' request is aborted via AbortController, so a stale response cannot overwrite the fresh one