javascript

name	javascript
description	JavaScript best-practices and rule enforcement — naming conventions, modern syntax idioms, `this`-handling, module structure, array/iteration performance, and nullability. Applies to plain JavaScript and is the foundation TypeScript builds on. TRIGGER when: language (JavaScript, JS, .js, .mjs, .cjs, Node.js, browser JS, ES modules, ESM, CommonJS), syntax (const/let, destructuring, template literals, optional chaining, nullish coalescing, arrow functions), patterns (this binding, callback, detached method, pure function vs method, module imports, barrel file, index.js), performance (array chains, filter().map(), intermediate arrays, hot path, GC pressure), nullability (null vs undefined, absence, sentinel value, == null check), naming (camelCase, PascalCase, kebab-case, boolean prefix), ask (idiomatic JavaScript, JS conventions, JS best practices, JS code review). ALSO APPLIES to TypeScript — it is the foundation TS builds on; load it alongside `typescript` on `.ts`/`.tsx`. For type-specific rules (type assertions `as T`, interfaces, generics, `readonly` modifier, `as const`, return type annotations) the `typescript` skill adds guidance on top. DO NOT USE as the primary skill for type-system questions (discriminated unions, generics, `as`, interfaces, narrowing) → route to `typescript` / `typescript-type-system`; this skill still applies underneath for naming and JS idioms.
user-invocable	false

JavaScript

Conventions and rules for idiomatic JavaScript. TypeScript builds on these — when working in TS, apply both this skill and typescript.

Rules (always apply)

Rule	File
Use JavaScript general conventions (naming, const/let, destructuring, template literals)	rules/js-general-conventions.md
Prefer explicit context (params) over implicit this	rules/prefer-explicit-context-over-this.md
Do not use barrel files (index.js/index.ts re-exports)	rules/no-barrel-files.md
Avoid intermediate arrays on hot paths (filter().map() chains)	rules/avoid-intermediate-arrays.md
undefined for absence, null for API/external contracts	rules/null-undefined.md

Read On Demand

• ECMAScript edition history (ES1 1997 → ES2025): see references/ecmascript-history.md. Use when judging which edition first shipped a feature, what needs a polyfill on older runtimes, or which syntax is safe for a target environment.

Specialist Skills

Situation	Skill	Why
TypeScript-specific features (types, generics, as const, readonly)	typescript	Type-system rules on top of JS conventions
Function composition, pipe, currying, FP patterns	composing-software	FP-flavored design beyond raw JS idioms
OOP / SOLID / design patterns	oop-principles	Class-based architecture