Question 1

Build a Notification Badge

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. Assumes basic HTML, CSS and JavaScript; React ideas are explained as they come up. **Difficulty:** Easy > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The Verified output was produced by mounting the solution with React 19.3.1 inside in jsdom and driving it with clicks and key presses. ## 1. Why This Even Matters — A Story First A post

Question 2

Build an Avatar Group

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. Assumes basic HTML, CSS and JavaScript; React ideas are explained as they come up. **Difficulty:** Easy > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The Verified output comes from mounting the solution with React 19.3.1 inside in jsdom. jsdom never downloads images and has no layout, so the image error was fired by the driver and the o

Question 3

Build a Dark Mode Toggle

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. You know useState and have seen useEffect; browser APIs like matchMedia and localStorage are new. **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 exact words an interviewer listens for. All code comes from the runnable solution next to this tutoria

Question 4

Build a Like Button

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. You know basic React state; promises and async code are still a little fuzzy. **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 exact words an interviewer listens for. All code comes from the runnable solution next to this tutorial, and the output in section 6 was produced by actually running it on Re

Question 5

Build a Counter component

Accepted Answer

**Target Audience:** Beginners preparing for their first frontend machine coding round. You know a little HTML and JavaScript; React is new or rusty. **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 exact words an interviewer listens for. All code comes from the runnable solution next to this tutorial, and the output in section 6 was produced by actually running it on React 19

Question 6

Build a Progress Bar

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. You need basic React (props, `useState`); timers in effects and the ARIA 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 from React 19.3.1 in StrictM

Question 7

Build a Traffic Light

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. You know a little JavaScript and React; state machines, timeouts, refs and effect cleanup are explained from zero. **Difficulty:** Easy > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary interviewers expect. Every output under "Verified" was printed by running this exact solution on React 19.3.1 inside in jsdom. ## 1. Why

Question 8

Build a Toggle Switch

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. You know basic React props and state; accessibility attributes are new territory. **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 exact words an interviewer listens for. All code comes from the runnable solution next to this tutorial, and the output in section 6 was produced by actually running it o

Question 9

Build a Temperature Converter

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. You know useState and controlled inputs; designing state for two inputs that depend on each other is the new part. **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 exact words an interviewer listens for. All code comes from the runnable solution next to this tutorial, and the output in s

Question 10

Build a Segmented Control

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. You need basic React (props, `useState`); controlled components and the radio group pattern 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 from React 19.3.1

FRONTEND MACHINE CODINGDECODED.

Easy

Build a Notification Badge

Build an Avatar Group

Build a Dark Mode Toggle

Build a Like Button

Build a Counter component

Build a Progress Bar

Build a Traffic Light

Build a Toggle Switch

Medium

Build a File Explorer Toolbar — Breadcrumbs, Search & Context Menu

Build a Color Picker

Build a Lazy-loaded Image

Build an Image Carousel

Build dependent (Country–State) dropdowns

Build a Search Bar with History

Build a Nested Comments widget

Build Tic-Tac-Toe

Hard

Build an E-commerce Product Filter grid

Build a File Explorer with Nested Drag-and-Drop

Build a Virtualized List

Build a Dual Range (price) Slider

Build Nested Checkboxes (tri-state)

Build a Calendar / Date Picker

Build a Kanban board with drag and drop

Build a data-fetching hook with caching, deduplication and retry