---
title: "Happy Path 81: TypeScript and effects"
description: "Michael Arnaldi describes Effect's TypeScript design and its typed outputs, errors, and requirements."
group: source
speaker: "Michael Arnaldi"
date: 2024-04-05
url: https://youtu.be/gc5P36t6kD0
sources:
  - https://youtu.be/gc5P36t6kD0
---

# Happy Path 81: TypeScript and effects

Michael traces Effect to a small fintech team that needed maintainable TypeScript and describes adapting ZIO ideas to TypeScript's type system and execution model. [05:43](https://youtu.be/gc5P36t6kD0?t=343) [10:51](https://youtu.be/gc5P36t6kD0?t=651) [24:24](https://youtu.be/gc5P36t6kD0?t=1464)

He describes an Effect by its output, predictable failures, and requirements. Layers let tests replace dependencies, while the type system narrows errors as they are handled. [33:34](https://youtu.be/gc5P36t6kD0?t=2014) [49:15](https://youtu.be/gc5P36t6kD0?t=2955)