javascriptAsync race conditionHard

Names come back in finishing order, not input order

Time: 0:00

BugFind the bug and fix the code

What it should do

labelAll(items) returns the names in the same order as the input, however long each one takes. Example: await labelAll([{ name: "a", ms: 20 }, { name: "b", ms: 1 }]) → ["a", "b"].

What happens instead

await labelAll([{ name: "a", ms: 20 }, { name: "b", ms: 1 }]) gives ["b", "a"].

const delay = (ms) => new Promise((r) => setTimeout(r, ms));

async function labelAll(items) {
    const out = [];
    await Promise.all(
        items.map(async (item) => {
            await delay(item.ms);
            out.push(item.name);
        })
    );
    return out;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the async and race conditions pattern

A missing await, results in the wrong order, and updates that overwrite each other under load.

Learn the async and race conditions pattern Step through your own code

<iframe src="https://trybughunt.com/embed/5222eae6-b9f8-4966-bd1d-d819a429a72a" title="Debugging challenge: Names come back in finishing order, not input order" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe> <p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/5222eae6-b9f8-4966-bd1d-d819a429a72a">TryBugHunt</a></p>

const delay = (ms) => new Promise((r) => setTimeout(r, ms)); async function labelAll(items) { const out = []; await Promise.all( items.map(async (item) => { await delay(item.ms); out.push(item.name); }) ); return out; }

Names come back in finishing order, not input order

What it should do

What happens instead

More async and race conditions to practise

Related errors

Names come back in finishing order, not input order

What it should do

What happens instead

More async and race conditions to practise

Related errors