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name: javascript-best-practices description: Idiomatic JavaScript patterns and conventions for maintainable existing code. Use when reviewing or refactoring JavaScript language patterns; defer project scaffolding, dependency setup, and tool configuration. metadata: triggers: files: - '/*.js' - '/*.mjs' keywords: - module - import - export - error - validation

JavaScript Best Practices

Priority: P1 (HIGH)

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 & Reference

See references/REFERENCE.md for constants, custom errors, async patterns, and module structure examples.

Related Topics

language | tooling

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• Naming

• index.js

• Additional task-grounded exact anchors: Comments