Writing Your First TurboModule in Swift

Teachers

Oskar Kwaśniewski

Software Developer

Callstack

React Native’s New Architecture makes TurboModules the default path for extending functionality. In this tutorial, Oskar walks through the full workflow: bootstrapping the project, exploring Codegen output, writing the Swift implementation, adding an Objective‑C bridge, and verifying the module inside a real app.

Bootstrapping the library with React Native Builder Bob

Oskar starts by creating an Expo project and using Builder Bob to scaffold a TurboModule library. This generates platform folders, a starter TypeScript spec, and default native code. Highlight the moment where he swaps the default multiply method for the Local Storage API (setItem, getItem, removeItem, clear).

Understanding the TypeScript spec and Codegen contract

The TypeScript spec defines the contract between JS and native. Codegen reads this file during pod install to produce Objective‑C/C++ headers that ensure type‑safe communication. Oskar shows where these headers live in Xcode and how they directly mirror the TypeScript definitions.

Navigating generated code in Xcode

Once expo prebuild and pod install run, the iOS folder appears with generated native targets. Oskar demonstrates how to locate the TurboModule inside the Pods hierarchy and why Xcode must build once before symbols resolve.

Implementing the business logic in Swift

The core logic lives in Swift: a NativeLocalStorage class backed by UserDefaults with a custom suite name. Oskar walks through the implementation of each method, including potential pitfalls (Swift types unsupported by Objective‑C).

Bridging Swift to Objective‑C

TurboModules require an Objective‑C layer. Oskar shows how to import the generated Swift header, create an instance variable, initialize it in init, and forward calls from Objective‑C into Swift. He discusses why attributes like @objcMembers are required for visibility.

Testing the TurboModule in an Expo application

The episode concludes with adding simple UI buttons that call the TurboModule from JavaScript. Oskar demonstrates setting a value, retrieving it, and verifying persistence via breakpoints in Xcode.

Resources

Oskar Kwaśniewski on X and GitHub
Other episodes in this series
Tools & libraries:
- React Native Builder Bob
- Expo (for prebuild + testing)
- TurboModules (New Architecture)
- Codegen

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