typescript-rules

TypeScript/JavaScript Rules

These rules come from app/rules/typescript/ in ai-toolkit. They cover the project's standards for coding style, frameworks, patterns, security, and testing in TypeScript/JavaScript. Apply them when writing or reviewing TypeScript/JavaScript code.

TypeScript Coding Style

Strict Mode

• Always use strict: true in tsconfig.json.
• Never use any -- use unknown + type guards instead.
• Prefer interface over type for object shapes (extendable).
• Use as const for literal types and readonly tuples.

Naming

• PascalCase: types, interfaces, enums, classes, components.
• camelCase: variables, functions, methods, properties.
• UPPER_SNAKE: constants, env vars.
• Prefix interfaces with I only if project convention requires it.

Functions

• Prefer arrow functions for callbacks and inline.
• Use function declarations for hoisted, named functions.
• Max 3 parameters -- use options object beyond that.
• Always type return values for public/exported functions.

Imports

• Group: node builtins, external, internal, relative.
• Use type imports: import type { Foo } from './foo'.
• No barrel exports unless at package boundary.
• Prefer named exports over default exports.

Types

• Use discriminated unions over class hierarchies for state.
• Use readonly for arrays and objects that should not be mutated.
• Use satisfies operator to validate types without widening.
• Prefer unknown over any at API boundaries.
• Use template literal types for string patterns.

Avoid

• enum -- use as const objects or union types.
• namespace -- use ES modules.
• private keyword -- use # private fields.
• Non-null assertion ! -- use proper type narrowing.
• as type casting -- use type guards and narrowing.

Configuration

• Enable noUncheckedIndexedAccess for safer array/object access.
• Enable exactOptionalPropertyTypes to distinguish undefined from missing.
• Use moduleResolution: "bundler" for modern projects.
• Set isolatedModules: true for bundler compatibility.