# Typed Functions

Give a function's parameters and return value types, so TypeScript rejects a call with the wrong kind of argument before the code runs.

![Cheat sheet: Typed Functions](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/11/da0db3f9e6224493a07380e0c3efb8a3.webp)

- Category: TypeScript
- Level: Apprentice
- Tags: "string", "number and boolean", Type Annotation, Type Error, typescript
- Updated: November 3, 2026

Source: https://www.ask-codey.com/cheat-sheets/working-with-typescript-typed-functions-cheat-sheet