Question 1

Build a Minimal createStore() (Redux-Lite: dispatch, subscribe, reducers)

Accepted Answer

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

> **How to read this doc:** all 3 real behaviors — correct reducer-driven state updates, subscriber notification on every real dispatch, and a genuinely working unsubscribe that stops FUTURE notifications while state updates continue normally — were verified directly through a real dispatch sequence.

## 1. The problem, restated

A minimal store holds a single piece of state, updated ONLY

Question 2

Design a Simple In-Memory Key-Value Store With TTL Expiry (Mini-Redis)

Accepted Answer

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

> **How to read this doc:** the TTL expiry claim was verified with real, measured timing — a value genuinely present immediately after `set`, and genuinely `undefined` after the real TTL had elapsed, with the internal store's own size confirmed to shrink, proving lazy self-cleanup actually happened.

## 1. The problem, restated

A key-value store where each entry can optionally carry a TT

Question 3

Build a Deterministic Feature-Flag Bucketing Function (Consistent Hash-Based A/B Assignment)

Accepted Answer

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

> **How to read this doc:** both real requirements — genuine determinism (no storage needed) and accurate real distribution — were verified directly: 5 repeated calls for the identical user+flag pair, and a real, measured 29.91% actual bucket rate against a configured 30% target across 100,000 simulated users.

## 1. The problem, restated

Decide whether a given user falls into a feature

Question 4

Build a Minimal State Machine Runner (States, Transitions, Guards)

Accepted Answer

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

> **How to read this doc:** all 3 real behaviors this question tests — correct transitions, a guard genuinely BLOCKING a transition when its condition fails, and an unhandled event leaving state unchanged — were verified directly through a real, sequential traffic-light state machine.

## 1. The problem, restated

A state machine config declares, for each named state, which EVENTS it respon

Question 5

Implement a Circuit Breaker for Flaky API Calls

Accepted Answer

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

> **How to read this doc:** the full real state cycle — CLOSED, tripping OPEN after enough failures, a call while OPEN being rejected WITHOUT even invoking the real underlying function, and eventual recovery through HALF_OPEN back to CLOSED — was verified directly against a real, genuinely flaky function.

## 1. The problem, restated

Repeatedly calling a real, currently-failing downstream

JAVASCRIPT CODINGDECODED.

Medium

Build a Minimal createStore() (Redux-Lite: dispatch, subscribe, reducers)

Design a Simple In-Memory Key-Value Store With TTL Expiry (Mini-Redis)

Build a Deterministic Feature-Flag Bucketing Function (Consistent Hash-Based A/B Assignment)

Hard

Build a Minimal State Machine Runner (States, Transitions, Guards)

Implement a Circuit Breaker for Flaky API Calls