Question 1

Build a Skeleton Loader

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. You need basic React (props, `useState`, `useEffect`); data-loading patterns and the accessibility details are explained here. **Difficulty:** Easy > **How to read this doc:** Every idea is explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. Code excerpts are copied from the runnable solution; the Verified blocks are real output fr

Question 2

Build a Lazy-loaded Image

Accepted Answer

**Target Audience:** Frontend candidates preparing for a machine coding round. Assumes basic React (components, props, `useState`); every browser API is explained from zero. **Difficulty:** Medium > **How to read this doc:** Each idea is explained in plain words first, then tagged with 📌 Interview term: so you also learn the vocabulary an interviewer listens for. The output in section 6 was produced by actually running the solution on React 19.3.1, in jsdom and in headless Chromiu

Question 3

Build dependent (Country–State) dropdowns

Accepted Answer

**Target Audience:** Frontend candidates preparing for a machine coding round. You know a little HTML and JavaScript; no React form experience is assumed. **Difficulty:** Medium > **How to read this doc:** Every idea is explained in plain language first, then tagged with 📌 Interview term: so you also learn the exact words an interviewer listens for. Code excerpts are copied from the runnable solution, and the output in section 6 was produced by actually running it on React 19.3.1

Question 4

Build a debounced Search Bar

Accepted Answer

**Target Audience:** Frontend developers preparing for a machine coding round. Assumes basic React (components, `useState`), nothing about debouncing or request cancellation. **Difficulty:** Medium > **How to read this doc:** Every idea is explained in plain language first, then tagged with 📌 Interview term: so you also learn the exact words an interviewer listens for. The output in the Verified section was produced by actually running the solution on React 19.3.1 in jsdom with a

Question 5

Build an Image Gallery with lightbox

Accepted Answer

**Target Audience:** Frontend candidates preparing for a machine coding round. Assumes basic React (`useState`, props, refs); dialogs, focus management and portals are explained from zero. **Difficulty:** Medium > **How to read this doc:** Each idea is explained in plain words, then tagged with 📌 Interview term: so you learn the vocabulary an interviewer expects. The output in section 6 was produced by running the solution on React 19.3.1 in jsdom and in headless Chromium 141. ##

Question 6

Build an Autocomplete / Typeahead search

Accepted Answer

**Target Audience:** Frontend developers preparing for a machine coding round. Assumes basic React state and effects; keyboard navigation, caching and ARIA roles are explained from zero. **Difficulty:** Medium > **How to read this doc:** Every idea is explained in plain language first, then tagged with 📌 Interview term: so you also learn the exact words an interviewer listens for. The Verified output was produced by running the solution on React 19.3.1 in jsdom with a scripted dri

Question 7

Build Infinite Scroll with IntersectionObserver & Skeleton

Accepted Answer

**Target Audience:** React developers who have built (or read) [infinite scroll with a scroll listener](/interview-question/build-infinite-scroll) and want the IntersectionObserver version with skeleton loading cards. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The Verified section has two parts. In jsdom, which has no IntersectionObserver, the driver installed a small stub and decided by hand when the sentinel was visi

Question 8

Build a Job Board (paginated fetch)

Accepted Answer

**Target Audience:** Developers preparing for a frontend machine coding round who know useState and useEffect and want to handle a two-step paginated fetch with loading, errors and retries properly. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Code excerpts are copied from the runnable solution, and the Verified section quotes what it printed on React 19.3.1. The Hacker News API is **simulated**

Question 9

Build Infinite Scroll

Accepted Answer

**Target Audience:** React developers new to infinite scrolling who know useState and useEffect and want to build it from first principles with a scroll listener. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The Verified output was produced by running the solution on React 19.3.1 under StrictMode in jsdom, with the scroll container given a fixed clientHeight and a content-based

Question 10

Build a Todo App with Pagination, Filters & Optimistic Updates

Accepted Answer

**Target Audience:** Developers who can already build a local todo list (see [Build a Todo List](/interview-question/build-a-todo-list)) and now need to talk to a slow, unreliable server. Assumes useState, useEffect and keys. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary interviewers listen for. Every code excerpt is copied from the runnable solution, and the Verified section q

FRONTEND MACHINE CODINGDECODED.

Easy

Build a Skeleton Loader

Medium