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

Implement a Double-Ended Queue (Deque) From Scratch

Accepted Answer

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

> **How to read this doc:** the ~22x speedup figure below is a real, direct measurement on a real 20,000-element deque, not a theoretical Big-O claim taken on faith.

## 1. The problem, restated

Implement a data structure supporting `pushFront`, `pushBack`, `popFront`, and `popBack` — all genuinely O(1), not just "fast enough in practice."

## 2. Clarifying questions a strong candidate ask

Question 3

Document tree depth check

Accepted Answer

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

> **How to read this doc:** every reported depth value below was computed against a real jsdom tree with an explicitly known shape, then checked by hand against that known shape — not assumed correct from the code alone.

## 1. The problem, restated

Given any DOM node, compute the length of the longest path from that node down to one of its own leaves, counting the starting node itself as

Question 4

Custom getElementById traverse

Accepted Answer

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

> **How to read this doc:** the "returns the same real node" claim was verified directly by reference-comparing the hand-written result against the actual, real `document.getElementById` in a real jsdom document — not assumed from reading the code.

## 1. The problem, restated

Given a root DOM node and a target id, walk the tree by hand (without using `getElementById`/`querySelector` inter

Question 5

Wire Up Debounced Resize and Throttled Scroll Handlers on a Real Component

Accepted Answer

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

> **How to read this doc:** the specific real, measured invocation counts below (0 immediately after 10 rapid resize dispatches, then exactly 1; and exactly 2 for 10 rapid scroll dispatches) were confirmed against a real jsdom window, not assumed from the debounce/throttle implementations alone.

## 1. The problem, restated

Attach a debounced `resize` handler and a throttled `scroll` han

Question 6

Priority queue binary heap

Accepted Answer

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

> **How to read this doc:** the real, defining correctness property of a heap — that repeated `extractMin()` calls always return values in genuinely sorted order, regardless of the original INSERTION order — was verified directly with a real, randomly-shuffled 9-number sequence.

## 1. The problem, restated

A binary min-heap is a complete binary tree (stored efficiently as a plain array,

Question 7

DOM event delegation target

Accepted Answer

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

> **How to read this doc:** the entire real point of delegation — that it correctly handles elements added to the DOM AFTER the listener was attached — was verified directly against a real jsdom container, not just asserted as a theoretical benefit.

## 1. The problem, restated

Rather than attaching a separate real listener to every individual matching element (which would miss any eleme

Question 8

Custom getElementsByClassName traverse

Accepted Answer

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

> **How to read this doc:** correctness was verified the strongest possible way — by comparing the custom implementation output DIRECTLY against the REAL, native `getElementsByClassName` on the identical real DOM tree, not just checking it against a hand-written expected list.

## 1. The problem, restated

Recursively walk a DOM subtree starting from a given root, collecting every descend

Question 9

DOM offset absolute coordinate

Accepted Answer

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

> **How to read this doc:** the summing algorithm was verified directly against a real, deliberately 3-level-deep offsetParent chain, confirming the exact expected combined coordinate rather than just describing the approach.

## 1. The problem, restated

`element.offsetTop`/`offsetLeft` are each relative only to the element's own IMMEDIATE `offsetParent` — not the whole document — so com

Question 10

Implement Fisher-Yates Shuffle (in-place, unbiased)

Accepted Answer

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

> **How to read this doc:** "unbiased" is a claim about a distribution, so it was measured, not asserted. With a seeded PRNG (so the numbers are reproducible), 600,000 shuffles of `[1,2,3]` were counted per permutation for the correct algorithm and two plausible-looking wrong ones; a chi-square test was then repeated over 200 different seeds.

## 1. The problem, restated

Produce a permut

JAVASCRIPT CODINGDECODED.

Easy

Fetch wrapper auto-retry

Implement a Double-Ended Queue (Deque) From Scratch

Document tree depth check

Custom getElementById traverse

Medium

Wire Up Debounced Resize and Throttled Scroll Handlers on a Real Component

Priority queue binary heap

DOM event delegation target

Custom getElementsByClassName traverse

DOM offset absolute coordinate

Implement Fisher-Yates Shuffle (in-place, unbiased)

Hard

DOM select elements custom selector

Query text highlighter

Find nearest common ancestor node

Virtual DOM diff algorithm

Virtual DOM element mapper

Implement a Virtualized List That Renders Only Visible Rows

Implement a Drag-and-Drop List Reordering Utility Without a Library