Question 1

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

Question 2

Build a Transfer List

Accepted Answer

**Target Audience:** Frontend developers preparing for a machine coding round. Assumes React state, props and lists; derived state, sets and the indeterminate checkbox 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 (StrictMode) in jsdom

Question 3

Build a Data Table with sorting and filtering

Accepted Answer

**Target Audience:** Developers preparing for a frontend machine coding round who know React state and lists and want to build a correct, reusable sortable and filterable table. **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 while a script clicked headers, typed and changed filters. ## 1. Why This Even Matt

Question 4

Build an E-commerce Product Filter grid

Accepted Answer

**Target Audience:** Developers preparing for a senior frontend machine coding round. Assumes React state, effects and list rendering; the derived-state ideas are explained from scratch. **Difficulty:** Hard > **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 while a script ticked filters, typed prices and removed chips. The catalogue

Question 5

Build a Data Table with Virtualized Rows, Sorting & Filtering

Accepted Answer

**Target Audience:** React developers who can build a basic sortable table (the medium version is [Build a Data Table with sorting and filtering](/interview-question/build-a-data-table-with-sorting-and-filtering)) and a windowed list ([Build a Virtualized List](/interview-question/build-a-virtualized-list)), and now need both at 20,000 rows. **Difficulty:** Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The Verified output was produced by r

Question 6

Build @Mentions in a textarea

Accepted Answer

**Target Audience:** Frontend developers preparing for a harder machine coding round. Assumes React hooks; text selection APIs, the mirror-div technique and the ARIA pattern are explained from zero. **Difficulty:** Hard > **How to read this doc:** Each idea in plain words first, then a 📌 Interview term: callout. The text logic was run with node and the component was driven on React 19.3.1 in jsdom (section 6). jsdom has no layout engine, so the pixel position of the menu was measu

FRONTEND MACHINE CODINGDECODED.

Medium