Codex skills for JavaScript
These skills work on the language and its packaging rather than one framework: modern built-ins, CommonJS to ESM moves, bundle size, Web Workers, semver and npm supply chain controls. Codex checks your browserslist and Node engines before using a newer API, and measures bundle weight and main-thread time before and after a change instead of assuming the win.
Start with these 3
- Modern JavaScript Newer built-ins, checked against your real targets Codex reads browserslist, engines and the transpiler setup before using any newer feature, separating syntax a compiler can down-level from runtime APIs that need real support. It swaps lodash and moment calls for platform built-ins one call site at a time, flags semantic traps such as || versus ?? on zero, and drops a dependency only when nothing still imports it.
- Bun Runtime Adopt Bun without surprise Node fallbacks Codex adopts Bun one layer at a time, package manager, tests, then runtime, and checks what still runs on Node along the way. It commits the text bun.lock, lists trustedDependencies for packages that need postinstall, keeps tsc in CI because Bun strips types without checking, and serves HTTP with Bun.serve routes plus a clean SIGTERM stop. Known traps like auto-loaded .env files are called out.
- Deno 2 Apps Scoped permissions instead of -A everywhere Codex sets up Deno 2 projects with dependencies in deno.json, a frozen lockfile and least-privilege permission sets it discovers by running without -A and reading each denial. It handles npm packages that need node_modules or install scripts, keeps fmt, lint, check and test in one task, and treats deployment as a confirmed step on the current Deno Deploy rather than the retired Classic platform and deployctl.
23 more JavaScript skills
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Node.js Streams
Flat memory for files of any size -
Node ESM Migration
From require to import without breaking consumers -
Node.js Profiling
Classify the slowdown, then profile the right thing -
Hono Edge API
One typed Hono app for Workers, Bun, Deno and Node -
ESLint Setup
Flat config that lints the files you think it does -
Codex SDK Automation
Drive Codex from TypeScript with real guardrails -
Dependency Upgrades
One major at a time, changelog read first -
Semantic Versioning
Major, minor or patch, decided against the real API -
Regex Crafting
Regexes with test tables and no catastrophic backtracking -
Express 5 API
Express services with one error path and typed input -
Gemini API
Gemini integrations on the current SDK and API -
Release Automation
Versions, changelogs and publishes nobody types -
Supply Chain Security
Install what you reviewed, ship what you can prove -
Jest Testing
Mocks that reset, timers that advance, Jest that exits -
Bundle Size Reduction
Find the kilobytes that matter and cut them -
Memory Leak Hunting
Snapshot, repeat, compare, follow the retainer -
Node CLI Tool Building
Node CLIs that run from npx and never hang in CI -
Fastify API
Schema-first Fastify with deliberate encapsulation -
NestJS Modules
Clean module graphs and DI that tests can swap -
TypeScript Declaration Files
Types that match the runtime and resolve everywhere -
LLM Streaming
Tokens that arrive live and stop when asked -
Cypress E2E
Aliased intercepts and cached sessions, no fixed waits -
Web Workers
Heavy work off the main thread, UI stays responsive
General skills with JavaScript guidance
Not built around JavaScript, but they include steps or tools for it. Not part of the install-all command.
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CSS Animations
Smooth motion with zero JavaScript -
AWS Lambda
Faster cold starts, no reprocessed batches -
Cloudflare Workers
Edge code that respects the isolate model -
Merge Conflict Resolution
Keep both intents, not just one side's text -
Dead Code Removal
Delete unused code with evidence, not hope -
Pre-commit Hooks
Hooks that fix staged files in seconds, not minutes -
Biome Setup
Swap ESLint and Prettier for Biome, knowing what you lose -
Codemods
Change 500 files with code you can rerun -
Monorepo Tooling
Cache hits you can trust, CI that builds only what changed -
Rust to WebAssembly
Coarse-grained Wasm modules that stay small -
Supabase Backend
Migrations, RLS and auth checks that hold up -
Neo4j Graph Modeling
Graph models built from the questions you ask
Every JavaScript skill in one command
Installs these 26 into ~/.agents/skills/. Add --project after -- to install into the current repository instead.
The installer is a 104-line POSIX shell script. It fetches the skills you name from codexskills.dev and unpacks each into its own folder in your skills directory. No sudo, no telemetry, and every skill page shows the full SKILL.md first. Read install.sh
curl -fsSL codexskills.dev/install.sh | sh -s -- javascript-modern bun-runtime deno-apps node-streams node-esm-migration node-profiling hono-edge-api eslint-setup codex-sdk-automation dependency-upgrades semantic-versioning regex-crafting express-api gemini-api release-automation supply-chain-security jest-testing bundle-size-reduction memory-leak-hunting cli-tool-building fastify-api nestjs-modules typescript-declaration-files llm-streaming cypress-e2e web-workers JavaScript FAQ
Is there a Codex skill for migrating a Node package from CommonJS to ESM?
Node ESM Migration chooses ESM-only or a dual build from the Node versions you support, taking into account that Node 20.19+ and 22.12+ can require() ES modules without flags. It replaces __dirname with import.meta.dirname, writes an exports map with types first and default last, and a bundled checker confirms every export target exists and loads before the packed tarball is tested from real ESM and CommonJS consumers.
Can Codex replace lodash and moment with built-in JavaScript?
Modern JavaScript swaps them for platform built-ins such as structuredClone, Object.groupBy, toSorted and Intl, one call site at a time, after reading browserslist, engines and the transpiler setup. It separates syntax a compiler can down-level from runtime APIs that need real support, and flags traps such as replacing || with ?? where a 0 or empty string used to fall back to the default.
Do these skills cover npm supply chain security?
Supply Chain Security applies controls in the order that stops real attacks: frozen lockfile installs, install scripts off by default, explicit registry scoping against dependency confusion, SHA-pinned GitHub Actions and release cooldowns. It then adds SBOMs, keyless cosign signatures and artifact attestations, and wires verification into the deploy path. Semantic Versioning complements it by classifying each change, including narrowed TypeScript types, before proposing a version bump.
How do I install all 26 JavaScript skills at once?
Pass every name to the installer in one command: curl -fsSL https://codexskills.dev/install.sh | sh -s -- javascript-modern bun-runtime deno-apps node-streams node-esm-migration node-profiling hono-edge-api eslint-setup codex-sdk-automation dependency-upgrades semantic-versioning regex-crafting express-api gemini-api release-automation supply-chain-security jest-testing bundle-size-reduction memory-leak-hunting cli-tool-building fastify-api nestjs-modules typescript-declaration-files llm-streaming cypress-e2e web-workers. Add --project right after -- to put them in the current repository's .agents/skills/ so your team gets them too.
Which JavaScript skill should I try first?
Modern JavaScript is the closest fit for most JavaScript work. Mention it with $javascript-modern in a prompt to load it on purpose; after that, Codex picks it up on its own whenever a task matches.