javascript-typescript-conventions

name	javascript-typescript-conventions
description	Tooling and conventions for JavaScript/TypeScript projects. Use when setting up new projects, configuring ESLint/Prettier alternatives, monorepos, or library publishing.

Coding Practices

Code Organization

• Single responsibility: Each source file should have a clear, focused scope/purpose
• Split large files: Break files when they become large or handle too many concerns
• Type separation: Always separate types and interfaces into types.ts or types/*.ts
• Constants extraction: Move constants to a dedicated constants.ts file

Runtime Environment

• Prefer isomorphic code: Write runtime-agnostic code that works in Node, browser, and workers whenever possible
• Clear runtime indicators: When code is environment-specific, add a comment at the top of the file:

// @env node
// @env browser

TypeScript

• Explicit return types: Declare return types explicitly when possible
• Avoid complex inline types: Extract complex types into dedicated type or interface declarations

Comments

• Avoid unnecessary comments: Code should be self-explanatory
• Explain "why" not "how": Comments should describe the reasoning or intent, not what the code does

Testing (Vitest)

• Test files: foo.ts → foo.test.ts (same directory)
• Use describe/it API (not test)
• Use toMatchSnapshot for complex outputs
• Use toMatchFileSnapshot with explicit path for language-specific snapshots

---

Tooling Choices

@antfu/ni Commands

Command	Description
ni	Install dependencies
ni <pkg> / ni -D <pkg>	Add dependency / dev dependency
nr <script>	Run script
nu	Upgrade dependencies
nun <pkg>	Uninstall dependency
nci	Clean install (pnpm i --frozen-lockfile)
nlx <pkg>	Execute package (npx)

Checking npm Package Versions

Use fast-npm-meta to look up the latest version of a package — it queries a small metadata endpoint instead of downloading the full registry payload (which can be megabytes per package).

nlx fast-npm-meta version vite              # 7.3.1
nlx fast-npm-meta version "nuxt@^3.5"       # 3.5.22 — range-aware
nlx fast-npm-meta version vite nuxt vue     # multiple at once
nlx fast-npm-meta version vite --json       # JSON for scripting
nlx fast-npm-meta full vite                 # full version list + dist-tags

Prefer this over npm view <pkg> version when you only need the latest version, and over reading package.json from the registry directly.

TypeScript Config

{
  "compilerOptions": {
    "target": "ESNext",
    "module": "ESNext",
    "moduleResolution": "bundler",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "resolveJsonModule": true,
    "isolatedModules": true,
    "noEmit": true
  }
}

ESLint Setup

// eslint.config.mjs
import antfu from '@antfu/eslint-config'

export default antfu()

When completing tasks, run pnpm run lint --fix to format the code and fix coding style.

Git Hooks

{
  "simple-git-hooks": {
    "pre-commit": "pnpm i --frozen-lockfile --ignore-scripts --offline && npx lint-staged"
  },
  "lint-staged": { "*": "eslint --fix" },
  "scripts": {
    "prepare": "npx simple-git-hooks"
  }
}

pnpm Catalogs

Use named catalogs in pnpm-workspace.yaml for version management:

Catalog	Purpose
prod	Production dependencies
inlined	Bundler-inlined dependencies
dev	Dev tools (linter, bundler, testing)
frontend	Frontend libraries

Avoid the default catalog. Catalog names can be adjusted per project needs.

---