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cal-diy-oidc/.claude/skills/vercel-react-best-practices/rules/js-hoist-regexp.md
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Udit Takkar 7a9fdd5a0c feat: add react best practises and web design skills (#26918)
## What does this PR do?

This PR adds https://vercel.com/blog/introducing-react-best-practices for your coding agent using `npx add-skill vercel-labs/agent-skills` command

The skills are added to `.claude/`, `.cursor/`, and `.opencode/` directories to provide React and Next.js performance optimization guidance for AI-assisted workflows.

## Updates since last revision

Addressed Cubic AI review feedback for issues with confidence >= 9/10:

- **rerender-dependencies.md** - Replaced `console.log(user.id)` with `fetchUserDetails(user.id)` to avoid logging sensitive information
- **server-after-nonblocking.md** - Removed `sessionCookie` from `logUserAction` call to avoid logging sensitive authentication data, added `await` to async call
- **bundle-conditional.md** - Added `loadError` state and `setLoadError` setter to fix undefined `setEnabled` reference
- **advanced-event-handler-refs.md** - Updated `useWindowEvent` handler signature to accept `Event` parameter and forward it to the stored handler
- **rerender-derived-state.md** - Closed `<nav>` elements in both examples for valid JSX

Fixes applied to both `.claude` and `.cursor` skill directories for consistency.

## Mandatory Tasks (DO NOT REMOVE)

- [x] I have self-reviewed the code (A decent size PR without self-review might be rejected).
- [x] N/A I have updated the developer docs in /docs if this PR makes changes that would require a [documentation change](https://cal.com/docs). If N/A, write N/A here and check the checkbox.
- [x] N/A, I confirm automated tests are in place that prove my fix is effective or that my feature works.

## How should this be tested?

These are documentation files for AI coding agents. No runtime testing required - review the markdown files to verify the example code snippets are correct.

## Checklist for human review

- [ ] Verify example code snippets in the skill files are syntactically correct
- [ ] Confirm the fixes don't introduce new issues in the documentation examples
- [ ] Check that `.claude` and `.cursor` directories have consistent content

---

Link to Devin run: https://app.devin.ai/sessions/f7f7e67fdeea4b22a4817d63ed9e1759
Requested by: unknown ()
2026-01-16 17:19:34 +05:30

1.0 KiB

title, impact, impactDescription, tags
title impact impactDescription tags
Hoist RegExp Creation LOW-MEDIUM avoids recreation javascript, regexp, optimization, memoization

Hoist RegExp Creation

Don't create RegExp inside render. Hoist to module scope or memoize with useMemo().

Incorrect (new RegExp every render):

function Highlighter({ text, query }: Props) {
  const regex = new RegExp(`(${query})`, 'gi')
  const parts = text.split(regex)
  return <>{parts.map((part, i) => ...)}</>
}

Correct (memoize or hoist):

const EMAIL_REGEX = /^[^\s@]+@[^\s@]+\.[^\s@]+$/

function Highlighter({ text, query }: Props) {
  const regex = useMemo(
    () => new RegExp(`(${escapeRegex(query)})`, 'gi'),
    [query]
  )
  const parts = text.split(regex)
  return <>{parts.map((part, i) => ...)}</>
}

Warning (global regex has mutable state):

Global regex (/g) has mutable lastIndex state:

const regex = /foo/g
regex.test('foo')  // true, lastIndex = 3
regex.test('foo')  // false, lastIndex = 0