If you've ever prepped for a frontend interview, you've probably hit this weird gap: LeetCode will happily grill you on binary trees and dynamic programming, but it has almost nothing to say about the thing you'll actually be asked to build in a real frontend interview — a debounced search box, a modal that traps focus correctly, a component that doesn't quietly re-render itself into a performance problem.
That gap is why I built ReactGrind.
What ReactGrind actually is?
ReactGrind is a coding practice platform built specifically around React — not algorithms, not data structures, just the actual behavior of React itself: hooks, rendering, state, effects, memoization, and the kind of edge cases that only show up once real user interaction is involved.
Every challenge comes with a real automated test suite, not a static answer key. You write a component, hit run, and the tests mount it, click it, type into it, and check the result — the same way a real pull request gets reviewed before it ships. If it passes, you know it actually works. If it fails, you know exactly where.
What's on there right now
50+ problems (adding questions daily) across Hooks & State, Custom Hooks, Performance, Context & Patterns, Forms & Events, and a FAANG-style Interview Set
A React Interview Prep section — 200+ questions with plain-English explanations, analogies, and code examples, not just one-line definitions
A free online React compiler/playground — no signup, no setup, just write and run React code instantly in the browser
A blog covering practical React engineering topics — React 19's actual production impact, MERN stack interview prep, and things like whether React counts as frontend or backend (yes, people really do ask that)
Why test-based practice, specifically?
Writing a debounced search box is easy. Writing one that still works when someone types fast, deletes everything mid-debounce, or unmounts the component while a timer is pending — that's the part that actually gets caught in code review, and it's the part a written answer key can't check for you. A real test suite catches it immediately, which is a much better habit to build than comparing your code to someone else's "correct" solution and hoping it's equivalent.
If you're prepping for a frontend role, or you just want to stay sharp on React outside of whatever you're building at work, it's free to start: reactgrind.com
Since this is early and actively evolving — if you try it and something feels off, missing, or like it should exist but doesn't, I'd genuinely like to hear it. Bug reports, feature ideas, "this problem's test cases are wrong," all of it is useful right now.
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