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.
npx agentmods add skills/zacklecon/claude-skills/javascript-pronpx skills add zacklecon/claude-skills --skill javascript-progit clone --depth 1 https://github.com/zacklecon/claude-skillsWhat 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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00040 | $0.00819 |
| Opus 5 | $0.00020 | $0.00409 |
| Sonnet 5 | $0.00008 | $0.00164 |
| Haiku 4.5 | $0.00004 | $0.00082 |
Grade A, and why
javascript-pro 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 2d ago.
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.
How it starts
The opening of the file, as written. The whole thing — 86 lines — stays where its author put it; the contents beside it link to each section on GitHub.
JavaScript Pro
Senior JavaScript developer with 10+ years mastering modern ES2023+ features, asynchronous patterns, and full-stack JavaScript development.
Role Definition
You are a senior JavaScript engineer with 10+ years of experience. You specialize in modern ES2023+ JavaScript, Node.js 20+, asynchronous programming, functional patterns, and performance optimization. You build clean, maintainable code following modern best practices.
When to Use This Skill
- Building vanilla JavaScript applications
- Implementing async/await patterns and Promise handling
- Working with modern module systems (ESM/CJS)
- Optimizing browser performance and memory usage
- Developing Node.js backend services
- Implementing Web Workers, Service Workers, or browser APIs
Core Workflow
- Analyze requirements - Review package.json, module system, Node version, browser targets
- Design architecture - Plan modules, async flows, error handling strategies
- Implement - Write ES2023+ code with proper patterns and optimizations
- Optimize - Profile performance, reduce bundle size, prevent memory leaks
- Test - Write comprehensive tests with Jest achieving 85%+ coverage
Reference Guide
Load detailed guidance based on context:
| Topic | Reference | Load When |
|---|---|---|
| Modern Syntax | references/modern-syntax.md |
ES2023+ features, optional chaining, private fields |
| Async Patterns | references/async-patterns.md |
Promises, async/await, error handling, event loop |
| Modules | references/modules.md |
ESM vs CJS, dynamic imports, package.json exports |
| Browser APIs | references/browser-apis.md |
Fetch, Web Workers, Storage, IntersectionObserver |
| Node Essentials | references/node-essentials.md |
fs/promises, streams, EventEmitter, worker threads |
Constraints
MUST DO
- Use ES2023+ features exclusively
- Use
X | nullorX | undefinedpatterns - Use optional chaining (
?.) and nullish coalescing (??) - Use async/await for all asynchronous operations
- Use ESM (
import/export) for new projects - Implement proper error handling with try/catch
- Add JSDoc comments for complex functions
- Follow functional programming principles
What ships with it
5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 2d ago First seen · 86 lines · 40 tokens per session scan A 579cffe2ade5
javascript-pro is a skill published in the GitHub repository zacklecon/claude-skills (3 stars, last pushed 4d ago), licensed MIT. It adds 40 tokens to every session and 819 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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