Guide · Agent skill
How to use the JavaScript Pro agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The JavaScript Pro skill is a set of written instructions and reference notes that tells an AI agent how to write, debug and refactor JavaScript the way a specialist would. It targets vanilla JavaScript, Node.js and browser code, with an emphasis on ES2023+ syntax, async/await with explicit error handling, and ES module conventions. This guide explains what the skill changes, how to install it, how to ask for it, and where it fits poorly.
JavaScript ProJeffallan/claude-skills · MIT Download the skill Quick start
- 1Download the ZIP. Get the javascript-pro ZIP from the skill's page on this directory.
- 2Unzip into a skills folder. Extract it to ~/.claude/skills/ for personal use, or to a project's .claude/skills/ folder for one project.
- 3Or upload in the Claude apps. In the Claude apps, open Settings → Capabilities → Skills and upload the skill.
- 4Check your project tooling. Make sure Node.js, npm, ESLint and Jest are available in the project you will work on.
- 5Make a natural request. Ask for a specific JavaScript task, naming the files or topic, such as async error handling or a Web Worker.
- 6Review the output and checks. Look at the code, the lint results and the Jest tests the agent reports before accepting the change.
What is an agent skill and what does this one make the agent do?
An agent skill is a folder containing a SKILL.md file and optional reference files. When you install it, an AI agent can load those instructions when a task matches the skill's description. The agent then follows the skill's rules instead of its default habits.
The javascript-pro skill asks the agent to analyse your package.json, module system and Node version first, then implement with modern syntax, handle async errors with try/catch, and prefer ESM for new projects. It also loads reference notes on modern syntax, async patterns, modules, browser APIs and Node essentials when they are relevant.
- Uses optional chaining (?.) and nullish coalescing (??), private class fields and other ES2023+ features
- Writes async code with try/catch and explicit handling of failed responses
- Follows ESM (import/export) conventions and avoids mixing require() with ESM
- Covers Fetch, AbortController, Web Workers, and Node fs/promises and streams
- Runs eslint --fix and Jest tests before finishing, and aims for 85%+ coverage
Install the javascript-pro skill
Download the ZIP for the skill from the directory page and unzip it. You can install it in one of two places. For a personal setup that applies across projects, unzip it into ~/.claude/skills/. For a single project, unzip it into that project's .claude/skills/ folder. The result should be a javascript-pro folder containing SKILL.md and a references folder.
If you use the Claude apps, you can instead upload the skill under Settings → Capabilities → Skills.
- Personal: ~/.claude/skills/javascript-pro/
- Project only: .claude/skills/javascript-pro/ inside your project
- Claude apps: Settings → Capabilities → Skills, then upload
Trigger the skill with natural requests
You usually do not need a special command. The skill is meant to be picked up when your request matches its description, which covers building vanilla JavaScript applications, Promise-based async flows, browser or Node.js performance, Web Workers, the Fetch API, and reviewing .js, .mjs or .cjs files. Name the topic clearly in your request so the match is obvious.
If the agent does not seem to use it, say so directly, for example by asking it to follow the javascript-pro skill.
- Review this file for async error handling: src/api/client.js
- Refactor this callback code to async/await with proper error handling
- Move this Node script from require() to ESM and check the imports
- Add a Web Worker to offload this parsing loop from the main thread
Example: a before and after from the skill's own patterns
The skill's examples contrast a fetch call that ignores failures with a version that checks response.ok, catches errors and returns a null guard. Asking the agent to review a function like the first one should produce something like the second.
Another pattern it applies is optional chaining with nullish coalescing, so that a missing nested property returns a default instead of throwing.
- Before: const response = await fetch(url); return response.json();
- After: check response.ok, wrap in try/catch, log the error and return a safe value
const city = user?.address?.city ?? "Unknown";What you need before using it
The skill itself runs no scripts and makes no network calls. The workflow, however, asks the agent to run eslint and Jest, so your target project needs Node.js and npm, with ESLint and Jest installed. Without them, the agent cannot complete the validation steps the skill describes.
The skill also assumes your project can use ESM. If it depends on CommonJS or TypeScript-only conventions, expect friction.
- Node.js and npm available in the project
- ESLint and Jest set up in the target project
- A project whose module system you are willing to keep consistent
Safety notes: scripts and network
According to the listing, the skill runs no scripts and uses no network access. It is a set of instructions and reference text. The commands the agent runs, such as eslint --fix and Jest, execute in your project through your normal tools, so review what the agent runs in your environment as you would for any agent task.
The skill's rules also tell the agent to check for memory leaks with DevTools or --inspect and to verify bundle size. Those checks depend on the tools you have available in the project.
- Scripts: none included in the skill, per the listing
- Network: none used by the skill itself
- Commands the agent runs come from the project's own linter and test setup
Tips for getting good results
The workflow is strict about validation. If you want quick throwaway code, say so, because the full lint, coverage and bundle checks add overhead. If you are reviewing existing code, state which files and which Node or browser targets matter so the agent can judge correctness against them.
Keep your project's module system stated in package.json. The skill checks it early, and a clear answer avoids mixed-module output.
- Name the files (.js, .mjs, .cjs) you want reviewed
- Tell the agent your Node version and browser targets
- Say when a quick script is enough so the full workflow is not forced on it
- Check that ESLint and Jest are configured before asking for tests
What people use it for
- Reviewing .js, .mjs or .cjs files for async error handling and missing null checks
- Converting CommonJS require() code to ESM import/export in a Node project
- Refactoring callback-style code to Promise-based async/await
- Adding a Web Worker or AbortController timeout to a browser feature
- Writing Jest tests for a new vanilla JavaScript module
Frequently asked questions
How do I install the javascript-pro skill?
Download the ZIP from the skill's page and unzip it into ~/.claude/skills/ for personal use, or into a project's .claude/skills/ folder. In the Claude apps, you can instead upload it under Settings → Capabilities → Skills.
Is the javascript-pro skill free?
The skill is published under the MIT licence, as stated on its page. The source does not mention pricing, so check the directory page for any other terms.
What does the JavaScript Pro skill require?
It requires Node.js and npm for running ESLint and Jest, and those tools need to be set up in the target project. The skill itself runs no scripts and uses no network.
Does the skill work with CommonJS or TypeScript projects?
Not well. The rules push ESM and forbid mixing module systems, so projects that depend on CommonJS or TypeScript-only conventions may clash with it.
Why does the agent run eslint and Jest?
The skill's workflow requires linting and tests before finishing, and asks for 85%+ Jest coverage. If you only want a quick script, this overhead may not suit you.
How is this different from just asking an AI for JavaScript help?
The skill gives the agent a fixed set of rules and reference notes on modern syntax, async patterns, modules and Node APIs, so its output follows consistent conventions. A general request without the skill has no such playbook.
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Our verdict
Use the JavaScript Pro skill if you build vanilla JavaScript or Node.js code in ESM and want consistent modern patterns, or a reviewer that checks async error handling in .js, .mjs and .cjs files. Pick something else if your project relies on CommonJS or TypeScript-only conventions, or if you mainly want quick throwaway scripts.
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