javascript-pro

javascript-pro is a skill for Claude Code, Codex from johnefemer/skillfish. It costs 0 tokens per session (9,507 once invoked), scanned A, original, no licence file.

A guide to modern JavaScript, the programming language commonly used in web browsers and server-side applications.

In plain words
What is it for?
Use it for ES2024 and newer JavaScript, event-loop behaviour, Web APIs, memory management, bundlers, and browser compatibility.
Why use it?
It helps developers understand language features, asynchronous execution, memory use, browser APIs, modules, and build configuration.

Skill for Claude CodeCodex

Which agent this was written for is unclear — body not stored (licence); the path alone says nothing.

Good fit Use it for ES2024 and newer JavaScript, event-loop behaviour, Web APIs, memory management, bundlers, and browser compatibility.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/johnefemer/skillfish/javascript-pro
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.

Any agent
npx skills add johnefemer/skillfish --skill javascript-pro
Clone the repo
git clone --depth 1 https://github.com/johnefemer/skillfish

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for javascript-pro

README.md
[![agentmods](https://agentmods.dev/badge/skills/johnefemer/skillfish/javascript-pro/github.svg)](https://agentmods.dev/skills/johnefemer/skillfish/javascript-pro)
Your own site
<a href="https://agentmods.dev/skills/johnefemer/skillfish/javascript-pro"><img src="https://agentmods.dev/badge/skills/johnefemer/skillfish/javascript-pro/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for javascript-pro

Your own site · 80×15
<a href="https://agentmods.dev/skills/johnefemer/skillfish/javascript-pro"><img src="https://agentmods.dev/badge/skills/johnefemer/skillfish/javascript-pro.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 9,507 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.
Origin unknown No closer match found 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 5.1 $0.00000 $0.09507
Opus 5.5 $0.00000 $0.03803
Sonnet 5.5 $0.00000 $0.01901
Haiku 4.5 $0.00000 $0.00951

Measured 2mo ago against content hash 818b7877a844, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

javascript-pro scanned grade A with 1 finding 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 2mo 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

const response = await fetch(nextUrl);
skills/javascript-pro/SKILL.md · 1,437 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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. 2mo ago First seen · 1,437 lines · 0 tokens per session scan A 818b7877a844

Subscribe to this mod's changes

javascript-pro is a skill published in the GitHub repository johnefemer/skillfish (4 stars, last pushed 4d ago), with no licence file. It costs nothing until one of its globs matches a file; then it loads 9,507 tokens. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

Related

javascript-pro compared with skills from other repositories

javascript-pro next to 6 skills from other repositories
ModTypeStarsLast pushLicenceScanTokensWorks with
javascript-projohnefemer/skillfishSkill44d agononeA0Claude Code, Codex
interactive-loginyc-software/qmSkill16kyesterdayMITA46Claude Code, Codex
pinchtab-mcppinchtab/pinchtabSkill11k10d agoMITA52Claude Code, Codex
azure-messaging-webpubsub-javamicrosoft/skillsSkill3.2kyesterdayMITA43Claude Code
cua-driverdavidondrej/skillsSkill4.3k3d agoMITA68Claude Code, Codex
open-design-browsercompozy/compozySkill2.8kyesterdayMITA56Claude Code, Codex
southwestborski/travel-hacking-toolkitSkill895yesterdayMITA40Claude Code