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Daily challenge

JavaScript Microtasks, Timers & AbortSignals

Test your mental model of microtask queue draining, promise resolution ordering, and structured cancellation.

Date: 2026-10-18Topic: javascriptDifficulty: intermediate6 min3 questions

2026-10-18javascript · intermediate · 6 minutes

0/3 answered

  1. Q1. What is the exact console output sequence when the following module executes?

    console.log('A');
setTimeout(() => console.log('B'), 0);
Promise.resolve()
  .then(() => {
    console.log('C');
    queueMicrotask(() => console.log('D'));
  })
  .then(() => console.log('E'));
console.log('F');

  2. Q2. How does AbortSignal.any([signalA, signalB]) behave when signalA is already aborted before AbortSignal.any is called?

  3. Q3. What does Object.groupBy(items, callback) return in ECMAScript 2024?