Question 1

Fetch wrapper auto-retry

Accepted Answer

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

> **How to read this doc:** every claim below — including the "404 does not retry" behavior — was verified against real, live network endpoints, not mocked.

## 1. The problem, restated

Wrap `fetch` so that a genuinely FAILED request is retried automatically, with an increasing delay between attempts (exponential backoff), up to a configured maximum number of retries.

## 2. Clarifying que

Question 2

Async filter utility

Accepted Answer

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

> **How to read this doc:** the real timing numbers below come from actually running both implementations against real, independently-delayed async checks — not calculated from theory alone.

## 1. The problem, restated

Implement `asyncFilter(items, predicate)` where `predicate` is an async function returning `Promise<boolean>` — the result should be a real array of only the items whose pr

Question 3

Build a Toast/Notification Queue That Shows One at a Time With Auto-Dismiss

Accepted Answer

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

> **How to read this doc:** the "never more than one active" claim was verified live, in a real browser, by sampling the actual DOM at multiple points in time — not asserted from reading the code alone.

## 1. The problem, restated

Build a queue where `enqueue(message)` can be called any number of times in quick succession, but the UI only ever shows ONE toast at a time — each auto-dismiss

Question 4

Implement sleep(ms) and delay with value

Accepted Answer

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

> **How to read this doc:** every claim here — including the busy-wait comparison — was actually run, not reasoned about in the abstract. Read the "Thought Process" section before the code; the reasoning is the point of this question, not just the final answer.

## 1. The problem, restated

Write `sleep(ms)`, callable as `await sleep(100)`, that pauses the CALLING async function for about `

Question 5

WebSocket reconnect logic

Accepted Answer

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

> **How to read this doc:** the exponential-doubling claim was verified directly with real, measured timing against a mock socket engineered to fail exactly 3 times before succeeding — not just asserted from the backoff formula.

## 1. The problem, restated

Wrap a real WebSocket factory so that on an unexpected `close` event, the wrapper automatically attempts to reconnect, waiting an ex

Question 6

Implement promiseRetry(fn, retries, delay) with exponential backoff

Accepted Answer

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

> **How to read this doc:** the exact real attempt counts below — 3 for the eventually-succeeding case, and `retries + 1` for the always-failing case — were confirmed with a real counter, not assumed from the recursive structure alone.

## 1. The problem, restated

`promiseRetry(fn, retries, delayMs)` calls `fn()`; on rejection, it waits `delayMs`, then tries again — doubling the delay ea

Question 7

Implement debounce() with leading/trailing and cancel/flush

Accepted Answer

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

> **How to read this doc:** all 5 real behavior modes below — trailing-only, leading-only, cancel, flush, and leading+trailing together — were verified directly with real, timed `setTimeout`-based tests, not just reasoned about from the code.

## 1. The problem, restated

`debounce(fn, wait, options)` returns a wrapped function that delays calling `fn` until `wait` ms of silence have pass

Question 8

Promise Retry with Backoff

Accepted Answer

### 💡 How to Think About This Problem
When implementing **Promise Retry with Backoff** in an interview, the interviewer evaluates your core JavaScript capabilities, syntax familiarity, and edge-case handling.

#### 1. Deconstructing the Requirements
To construct a robust solution:
* **Pre-conditions**: Handle empty collections or incorrect parameter types.
* **Core Logic**: Target the required functional transformation cleanly.

#### 2. Step-by-Step Breakdown

* **Step 1: Input Validation** - C

Question 9

Implement a Cancelable Promise (with CancelToken / AbortController)

Accepted Answer

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

> **How to read this doc:** the critical, real distinguishing claim — that cancellation genuinely stops the underlying work rather than merely having the caller ignore a stale, still-arriving result — was verified directly by measuring REAL elapsed time: the promise rejected in about 20ms, not anywhere near its original 1000ms delay.

## 1. The problem, restated

A GENUINELY cancelable asyn

JAVASCRIPT CODINGDECODED.

Easy

Fetch wrapper auto-retry

Async filter utility

Build a Toast/Notification Queue That Shows One at a Time With Auto-Dismiss

Implement sleep(ms) and delay with value

Medium

WebSocket reconnect logic

Implement promiseRetry(fn, retries, delay) with exponential backoff

Implement debounce() with leading/trailing and cancel/flush

Promise Retry with Backoff

Hard

Implement a Cancelable Promise (with CancelToken / AbortController)