# Javascript Best Practices

> Idiomatic JavaScript patterns and conventions for maintainable code. Use when this capability is needed.

- Skill: `tomevault-io/javascript-best-practices` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/javascript-best-practices`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/javascript-best-practices/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/javascript-best-practices

---


# JavaScript Best Practices

## **Priority: P1 (OPERATIONAL)**

Conventions and patterns for writing maintainable JavaScript.

## Implementation Guidelines

- **Naming**: `camelCase` (vars/funcs), `PascalCase` (classes), `UPPER_SNAKE` (constants).
- **Errors**: Throw `Error` objects only. Handle all async errors.
- **Comments**: JSDoc for APIs. Explain "why" not "what".
- **Files**: One entity per file. `index.js` for exports.
- **Modules**: Named exports only. Order: Ext -> Int -> Rel.

## Anti-Patterns

- **No Globals**: Encapsulate state.
- **No Magic Numbers**: Use `const`.
- **No Nesting**: Guard clauses/early returns.
- **No Defaults**: Use named exports.
- **No Side Effects**: Keep functions pure.

## Code

```javascript
// Constants
const STATUS = { OK: 200, ERROR: 500 };

// Errors
class APIError extends Error {
  constructor(msg, code) {
    super(msg);
    this.code = code;
  }
}

// Async + JDoc
/** @throws {APIError} */
export async function getData(id) {
  if (!id) throw new APIError('Missing ID', 400);
  const res = await fetch(`/api/${id}`);
  if (!res.ok) throw new APIError('Failed', res.status);
  return res.json();
}
```

## Reference & Examples

For module patterns and project structure:
See [references/REFERENCE.md](references/REFERENCE.md).

## Related Topics

language | tooling

---
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