Functional Programming in TypeScript

Functional programming offers powerful tools for building robust, maintainable software, and Software Development as a whole has moved towards employing a functional style—yet comprehensive guides for normal work in real-world applications are still hard to find. This tutorial aspires to fill (a part of) this gap: It teaches functional programming patterns and shows you how to apply them immediately in your daily work, with TypeScript as a language.

We’ll start with the fundamentals: immutability, pure function, and function composition.
You’ll learn how model your data to make illegal states unrepresentable, how to push out your error types using Parse, don’t Validate, and how to move effects out of the core of your application. We tackle those while building a small frontend application using reduce functions over our state, and you’ll see how functional principles scale from small utilities to entire applications.

By the end, you’ll understand not only functional programming patterns, but how you can employ them in TypeScript development.

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Since this tutorial is only marginally relying on language features of TypeScript, large parts of this tutorial translate over relatively easy to other programming languages.

Beat Hagenlocher

https://bsky.app/profile/beathagenlocher.com

Beat Hagenlocher is a Software Architect at Active Group GmbH.

Always on the lookout for the perfect programming stack to code his projects in, he currently has conceded that TypeScript is actually “good enough for most things for now” and writes his frontend software with that.

Apart from writing software, he hosts Tü.λ - Functional Programming Night Tübingen and tends to his digital garden.

When not at the computer, he can be found doing sports, learning new skills or adding to his book list.