Question 1

Build a Read More / Show Less text component

Accepted Answer

**Target Audience:** Beginners preparing for a frontend machine coding round. Assumes basic HTML 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 in jsdom and clicking through it with a script. jsdom has no layout engine, so the CSS line-clamp facts were measured separately in Chromium 141, and the

Question 2

Build a Dropdown Menu

Accepted Answer

**Target Audience:** Frontend candidates preparing for a machine coding round. Assumes basic HTML, JavaScript and React components with `useState`; everything else is explained here. **Difficulty:** Easy > **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. Every output quoted below was printed by the real solution, run on React 19.3.1 in jsdom and again in real Chrom

Question 3

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

Accepted Answer

**Target Audience:** Frontend candidates who can already render a recursive tree in React and want the "power user" layer on top. **Difficulty:** Medium > **How to read this doc:** Plain words first, then a 📌 Interview term: tag. This question assumes the tree itself; if recursion, `expanded` sets or immutable tree updates are new to you, start with [Build a File Explorer (tree view)](/interview-question/build-a-file-explorer-tree-view). Every snippet is from the runnable solution

Question 4

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 5

Build a Search Bar with History

Accepted Answer

**Target Audience:** Frontend developers preparing for a machine coding round. Assumes basic React state and events; `localStorage` and focus management 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 driver that typed, p

Question 6

Build a Command Palette (kbar / cmdk) with Fuzzy Search

Accepted Answer

**Target Audience:** Frontend developers preparing for a machine coding round. Assumes React hooks; fuzzy matching, the combobox pattern and focus management are explained from zero. **Difficulty:** Medium > **How to read this doc:** Each idea in plain words first, then a 📌 Interview term: callout with the precise vocabulary. The matcher was run directly with node, and the whole palette was booted on React 19.3.1 in jsdom and driven with real key presses; section 6 quotes that out

Question 7

Build a Tabs Component with URL Sync & Lazy Mounting

Accepted Answer

**Target Audience:** Developers who can already build an accessible tabs component and want the next step: URL state and lazy panels. If roles and roving tabindex are new to you, start with [Build a Tabs component](/interview-question/build-a-tabs-component). **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Code excerpts are copied from the runnable solution. The Verified blocks are real output: React 19.3.1 in StrictMode dr

Question 8

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 9

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 10

Build a Custom Multi-select Dropdown

Accepted Answer

**Target Audience:** Frontend developers preparing for a machine coding round. Assumes React state and props; sets, chips, focus handling and multi-select ARIA 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 driver that cl

FRONTEND MACHINE CODINGDECODED.

Easy

Build a Read More / Show Less text component

Build a Dropdown Menu

Medium

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

Build dependent (Country–State) dropdowns

Build a Search Bar with History

Build a Command Palette (kbar / cmdk) with Fuzzy Search

Build a Tabs Component with URL Sync & Lazy Mounting

Build a debounced Search Bar

Build an Autocomplete / Typeahead search

Build a Custom Multi-select Dropdown

Hard

Build an E-commerce Product Filter grid

Build a Data Table with Virtualized Rows, Sorting & Filtering

Build a Variable-Size Virtualized Feed (Dynamic Heights)

Build @Mentions in a textarea

Build a Combobox (search + select)