Question 1

Sync State Across Tabs Using the storage Event

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 the storage event genuinely never fires in the SAME document that made the write — was verified directly, live, in a real browser, not assumed from documentation.

## 1. The problem, restated

Using only `localStorage` and its associated real browser event, make every OTHER open tab of the same app a

Question 2

Polyfill Function.prototype.call and apply

Accepted Answer

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

> **How to read this doc:** the real, subtle correctness detail this question specifically tests — that the internal technique used to invoke the function must leave NO trace on the real context object afterward — was verified directly: a real, live check confirmed no extra enumerable property remained on the context after `myCall` completed.

## 1. The problem, restated

Implement `.call`/

Question 3

Implement compose() and pipe() for function composition

Accepted Answer

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

> **How to read this doc:** the claim that compose and pipe produce the IDENTICAL final result when given the same functions in REVERSED order was verified directly with real computed output (64, both ways, for the same input).

## 1. The problem, restated

`compose(f, g, h)(x)` applies RIGHT TO LEFT: `f(g(h(x)))`. `pipe(f, g, h)(x)` applies LEFT TO RIGHT: `h(g(f(x)))`... more precisely,

Question 4

Polyfill Function.prototype.bind (with new support)

Accepted Answer

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

> **How to read this doc:** the real, defining subtlety this question tests — that a bound function used as a CONSTRUCTOR must correctly IGNORE the pre-bound `this`, using the newly-created instance instead — was verified directly: a real `new BoundPoint(10)` call correctly produced a genuine `Point` instance, not an object using the bound `thisArg`.

## 1. The problem, restated

`bind` r

Question 5

Safely Merge Untrusted Input Into an Object Without a Prototype-Pollution Vulnerability

Accepted Answer

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

> **How to read this doc:** this is not a theoretical concern — the actual vulnerability was demonstrated LIVE, directly: a naive merge (with no key-blocking guard) was shown to genuinely pollute the real, GLOBAL `Object.prototype` with a real, malicious payload, while the safe version left it completely untouched, verified via a real, direct check against a freshly-created `{}`.

## 1. The

JAVASCRIPT CODINGDECODED.

Easy

Sync State Across Tabs Using the storage Event

Polyfill Function.prototype.call and apply

Medium

Implement compose() and pipe() for function composition

Polyfill Function.prototype.bind (with new support)

Hard

Safely Merge Untrusted Input Into an Object Without a Prototype-Pollution Vulnerability