TypeScript/JavaScript Development Guide

Code Style

• •Use strict TypeScript ("strict": true in tsconfig.json)
• •Prefer const over let, avoid var
• •Use async/await over raw Promises
• •Export types alongside functions

Common Patterns

• •Use discriminated unions for state management
• •Prefer composition over inheritance
• •Use unknown instead of any when type is uncertain

Testing

• •Co-locate tests with source files or use __tests__ directories
• •Use descriptive test names: it('should return empty array when input is null')
• •Mock external dependencies, not internal modules

Error Handling

• •Create custom error classes extending Error
• •Always include error context in messages
• •Use Result pattern for expected failures

Biome/ESLint

• •Run biome check --apply . before committing
• •Address all lint warnings, don't disable rules without justification