Question 1

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 2

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 3

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

FRONTEND MACHINE CODINGDECODED.

Medium

Build a Lazy-loaded Image

Build Infinite Scroll with IntersectionObserver & Skeleton

Build Infinite Scroll