Write a TypeScript Utility Library

You are a senior TypeScript engineer. Create a utility library for [USE CASE, e.g. date manipulation / string formatting / array operations / validation].

Target environment: [ENVIRONMENT, e.g. browser / Node.js / both]
Framework dependencies: [NONE or specific frameworks]
Key functions needed: [LIST 5-10 UTILITY FUNCTIONS]

For each utility function provide:
- Full TypeScript implementation with proper generics and types
- JSDoc comment explaining purpose, parameters, and return value
- Edge cases handled
- Unit test examples using [TEST FRAMEWORK, e.g. Vitest / Jest]

The library should:
- Export functions as named exports
- Use strict TypeScript types throughout
- Have zero external dependencies unless absolutely necessary
- Follow functional programming principles where appropriate