---

name: javascript-practices description: JS/TS conventions for syntax, modules, and types. Use when writing or reviewing JavaScript/TypeScript code.

JavaScript/TypeScript Practices

Conventions for JS/TS syntax, modules, types, and runtime behavior.

Quick Start

Copyimport * as path from "@std/path"; // namespace import
import { utils } from "./utils.ts"; // explicit extension

export function buildConfig() {} // direct named export
const port = config.port ?? 8000; // nullish coalescing

Key Principles

Modules: Direct named exports, namespace imports, explicit .ts extensions

Syntax: const over let, always semicolons, === strict equality, ?? over ||

Types: Number() over +, instanceof over typeof, prefer null over undefined

Runtime: import.meta.dirname, globalThis over window, optional projectRoot params

Async: Use return await consistently for better stack traces and correct error handling

Avoid: eval, prototype mutation, truthy/falsy checks on non-booleans

References

See rules.md for complete guidelines with examples.