Question 1

Implement once(func) — ensure a function runs only once

Accepted Answer

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

> **How to read this doc:** every claim — including the underlying call-count and `this`-binding checks — was actually run, not asserted.

## 1. The problem, restated

Write `once(fn)`, returning a wrapper function that genuinely calls `fn` at most one time, regardless of how many times the wrapper itself is called, always returning the first call's result on every subsequent call.

## 2. C

Question 2

Implement a Memoized Selector That Only Recomputes When Its Specific Inputs Change (Reselect-Style)

Accepted Answer

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

> **How to read this doc:** the whole real point of this pattern — genuinely SKIPPING recomputation, verified by checking that the exact SAME array reference is returned, not merely an equal-looking new one — was confirmed directly, not assumed from the caching logic alone.

## 1. The problem, restated

`createSelector(inputSelectors, resultFn)` returns a memoized selector function: each

Question 3

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 4

Implement TimeLimitedCache (LeetCode 2622) with expiry

Accepted Answer

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

> **How to read this doc:** the version here stores an `expiresAt` timestamp and checks it lazily, with an injectable clock so every edge case is tested deterministically. The obvious alternative, one `setTimeout` per entry, was also tested and shown to have two real defects: it keeps the Node process alive, and if the old timer is not cleared on overwrite it deletes the NEWER value early

Question 5

Implement memoize() with custom resolver and cache limit

Accepted Answer

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

> **How to read this doc:** the eviction claim — that exceeding `maxSize` genuinely forces a real recomputation on the next access to the evicted key — was verified directly with a real call counter, not just reasoned about from the `Map` insertion-order behavior.

## 1. The problem, restated

`memoize(fn, { resolver, maxSize })` returns a wrapped function that caches `fn`'s results by a

Question 6

Implement LRU Cache (get/put with O(1))

Accepted Answer

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

> **How to read this doc:** the classic answer is a hash map plus a doubly linked list. In JavaScript a plain `Map` already remembers insertion order, so the whole structure collapses to one `Map`: "delete then set" moves a key to the newest position, and the first key in iteration order is the least recently used. The LeetCode trace was reproduced, and 10x more operations were verified t

Question 7

Implement an LFU (Least Frequently Used) Cache

Accepted Answer

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

> **How to read this doc:** both real correctness requirements — frequency-based eviction AND the LRU tie-break among equally-frequent keys — were verified directly and SEPARATELY: one real test confirming the lower-frequency key was evicted, and a second, distinct real test confirming that among two keys with the IDENTICAL frequency, the older (least recently used) one was correctly evicte

JAVASCRIPT CODINGDECODED.

Easy

Implement once(func) — ensure a function runs only once

Medium

Implement a Memoized Selector That Only Recomputes When Its Specific Inputs Change (Reselect-Style)

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

Implement TimeLimitedCache (LeetCode 2622) with expiry

Implement memoize() with custom resolver and cache limit

Implement LRU Cache (get/put with O(1))

Hard

Implement an LFU (Least Frequently Used) Cache