javascript-performance

A set of JavaScript and TypeScript rules for finding common performance problems in React code. The rules apply to files ending in .js or .ts and include suggestions for reducing unnecessary rendering work.

In plain words
What is it for?
Use it to review React code for avoidable state changes, anonymous functions in render methods, missing memoization, and list-rendering improvements.
Why use it?
It flags patterns that may cause needless state updates, component re-renders, or inefficient rendering code during development.

Cursor rule for Cursor

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/abderrahimghazali/cursor-rules/javascript-performance
Clone the repo
git clone --depth 1 https://github.com/abderrahimghazali/cursor-rules

Made for: Cursor.

Per session 198 This file is loaded in full into every session.
When invoked 198 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin 100% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00198 $0.00198
Opus 5 $0.00099 $0.00099
Sonnet 5 $0.00040 $0.00040
Haiku 4.5 $0.00020 $0.00020

Measured yesterday against content hash 2055c06cc248, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

javascript-performance scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

This is a copy

100% identical to javascript-performance — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.cursor/rules/javascript-performance.mdc · 34 lines

What it actually says


description: JavaScript Performance Optimization globs: *.js, *.ts

JavaScript Performance Optimization

actions:

  • type: enforce conditions:

    • pattern: "\buseState\(([^)]*)\)" message: "Avoid unnecessary state updates."

    • pattern: "React\.memo\(" message: "Consider using React.memo() to optimize component re-renders."

    • pattern: "\b\(\)\s*=>\s*{" message: "Avoid using anonymous functions in render methods."

  • type: suggest message: | Performance tips:

    • Use memoization for expensive calculations.
    • Optimize FlatList with performance props.
    • Minimize unnecessary re-renders.

metadata: priority: high version: 1.0

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 34 lines · 198 tokens per session scan A 2055c06cc248

Subscribe to this mod's changes

javascript-performance is a cursor rule published in the GitHub repository abderrahimghazali/cursor-rules (2 stars, last pushed 1y ago), licensed MIT. It adds 198 tokens to every session, about $0.0010 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to javascript-performance, differing in 0 lines, and is treated as a copy.