---
title: "cnfast vs cn(): Is the 7x speedup real in React?"
url: https://daily.dev/posts/cnfast-vs-cn-is-the-7x-speedup-real-in-react--ljdnzcw2j
source_url: https://blog.logrocket.com/cnfast-vs-cn-react
type: article
source: "LogRocket"
published: 2026-08-24T08:09:27.925Z
updated: 2026-08-24T08:10:03.579Z
tags: ["javascript", "react", "tailwind-css", "shadcn"]
reading_time: 13
upvotes: 5
comments: 1
language: en
---

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# cnfast vs cn(): Is the 7x speedup real in React?

**[LogRocket](https://daily.dev/sources/logrocket)** · 13 min read · 5 upvotes · 1 comments

## Summary

A developer built a real dashboard app to test whether cnfast, a drop-in replacement for shadcn/ui's cn() utility claiming up to 7x speedups, actually improves performance in practice. Isolated microbenchmarks showed real gains (5.75x-7.19x in Node, only 2.12x-2.72x in Chrome due to V8's argument caching), and correctness was verified across 351 test cases with zero mismatches. But when measured inside actual React renders on a 500-row data grid, a 1,500-item virtual list, and SSR, the speedup shrank to noise-level differences (2ms on a 28ms render, dropped frames within run-to-run variance). The conclusion: cn() is such a tiny fraction of render cost that even a 7x faster version is imperceptible in real apps, and cnfast adds about 1KB to bundle size for a win most apps won't feel.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://blog.logrocket.com/cnfast-vs-cn-react>

## Questions this post answers

### Is cnfast actually faster than the standard cn() function used in shadcn/ui projects?

Yes in isolated microbenchmarks, but the gain is much smaller in real React apps. In Node, cnfast's call form measured 5.75x faster and its tagged-template form 7.19x faster than the standard clsx plus tailwind-merge cn(). In Chrome, where React actually runs, those numbers dropped to 2.12x and 2.72x because V8 already caches repeated call arguments.

_Developers choosing between styling utilities can weigh benchmark claims like this against real render costs on daily.dev._

### Does swapping cn() for cnfast noticeably speed up a React data grid or virtual list?

Barely. On a 500-row data grid with over 4,000 cn() calls per sort, render time dropped from 28.47ms to 26.37ms, about a 7.4% gain, while row-select re-renders showed no measurable difference. On a 1,500-item virtualized scroll, dropped frames fell from 92 to 88 on average, within run-to-run noise, since scroll cost is dominated by layout and paint, not class merging.

_Teams profiling React render bottlenecks can track findings like these on daily.dev before chasing a swap._

### Is cnfast a safe drop-in replacement for the standard shadcn cn() function in terms of output correctness?

Yes, testing across 351 argument groups covering real dashboard call sites, edge cases like arbitrary values and object syntax, and mixed permutations produced zero mismatches between cnfast and the standard clsx plus tailwind-merge implementation. Note it adds about 1KB gzipped to bundle size, and an open issue exists around its ClassValue type clashing with clsx's ClassDictionary in some Radix or Base UI render-function className patterns.

_Developers evaluating drop-in library swaps for shadcn projects can follow correctness reports like this on daily.dev._

## Community discussion

Top comments from developers on daily.dev.

**@masculin** · 0 upvotes

> So it’s not a big deal diff then, stick to the legacy cn unless you’re running a table within over 1K rows per page.

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---

Tags: [#javascript](https://daily.dev/tags/javascript), [#react](https://daily.dev/tags/react), [#tailwind-css](https://daily.dev/tags/tailwind-css), [#shadcn](https://daily.dev/tags/shadcn)

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