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 Minimal useState Hook Using Closures (How React's State Actually Persists Between Renders)

Accepted Answer

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

> **How to read this doc:** the core, often-confusing question this answers — "if a component is just a function that gets called again, HOW does state survive between calls?" — was verified directly by building the real mechanism and observing state genuinely persist across simulated re-renders.

## 1. The problem, restated

A React function component is, quite literally, just a plain fu

Question 3

Implement curry(func) with placeholder support

Accepted Answer

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

> **How to read this doc:** the real, defining placeholder-filling mechanism this question tests was verified across FOUR distinct real placement patterns — `fn(1, _, 3)(2)`, `fn(_, 2, 3)(1)`, `fn(_, _, 3)(1)(2)`, and `fn(_, _, 3)(1, 2)` — all correctly, genuinely producing the same result, `6`, confirming the placeholder's own position is respected regardless of how many placeholders exi

Question 4

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 5

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

JAVASCRIPT CODINGDECODED.

Easy

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

Medium

Implement a Minimal useState Hook Using Closures (How React's State Actually Persists Between Renders)

Implement curry(func) with placeholder support

Implement memoize() with custom resolver and cache limit

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