Question 1

Implement Promise.race()

Accepted Answer

**Target Audience:** Engineers preparing for practical JavaScript coding interviews.
**Difficulty:** Easy

> **How to read this doc:** the sharpest, most commonly-missed part of this question — that a REJECTION can win the race just as validly as a resolution — was verified directly, not assumed from the method's name.

## 1. The problem, restated

Implement `Promise.race(promises)`: returns a new promise that settles the instant the FIRST input promise settles, adopting that promise's own outco

Question 2

Implement Promise.all() from scratch

Accepted Answer

**Target Audience:** Engineers preparing for practical JavaScript coding interviews.
**Difficulty:** Medium

> **How to read this doc:** the "order is preserved regardless of completion order" claim — the single most commonly-missed detail in a naive first attempt — was verified directly with a slower promise listed BEFORE a faster one.

## 1. The problem, restated

Given an array of promises, return one promise that resolves with an array of ALL their results, in the SAME order as the input arr

Question 3

Implement Promise.any() with AggregateError

Accepted Answer

**Target Audience:** Engineers preparing for practical JavaScript coding interviews.
**Difficulty:** Medium

> **How to read this doc:** the real, defining difference from `Promise.race` this question tests — that an EARLIER rejection must be correctly IGNORED if a later promise still fulfills — was verified directly: with input `[rejectedPromise, fastFulfillment, slowFulfillment]`, the result correctly resolved with the fast fulfillment's value, never short-circuiting on the earlier rejection.

Question 4

Debounce async promise resolver

Accepted Answer

**Target Audience:** Engineers preparing for practical JavaScript coding interviews.
**Difficulty:** Medium

> **How to read this doc:** the "every pending caller resolves, not just the last one" requirement — the part a plain callback-based debounce cannot handle at all — was verified directly: 3 real calls in a burst, all 3 returned promises resolving to the identical final result.

## 1. The problem, restated

`debounceAsync(fn, wait)` wraps an async function: only the LAST call in a rapid bu

Question 5

Implement p-limit — concurrency limiter for async tasks

Accepted Answer

**Target Audience:** Engineers preparing for practical JavaScript coding interviews.
**Difficulty:** Medium

> **How to read this doc:** the "never more than N active at once" claim was verified directly with a real, live execution log across 5 real async tasks at a limit of 2, not just reasoned about.

## 1. The problem, restated

`pLimit(concurrency)` returns a function; wrapping any async task-returning function with it guarantees at most `concurrency` tasks run SIMULTANEOUSLY — additional ta

Question 6

Implement a minimal Promise/A+ (MyPromise) with then/catch

Accepted Answer

**Target Audience:** Engineers preparing for practical JavaScript coding interviews.
**Difficulty:** Hard

> **How to read this doc:** Promises/A+ is a small spec (a few rules about `then` plus one resolution procedure) and it has an official test suite, so this solution was not just demoed: it was run against `promises-aplus-tests` version 2.1.2 and passed all 872 tests. Then the design was stress-tested by removing ONE feature at a time and re-running the suite (each removal fails between 2 an

JAVASCRIPT CODINGDECODED.

Easy

Implement Promise.race()

Medium

Implement Promise.all() from scratch

Implement Promise.any() with AggregateError

Debounce async promise resolver

Implement p-limit — concurrency limiter for async tasks

Hard

Implement a minimal Promise/A+ (MyPromise) with then/catch