Compiling Scala.js to WebAssembly

Explore the groundbreaking implementation of WebAssembly compilation in Scala.js through this 39-minute conference talk from Scala Days 2025. Discover how Scala.js 1.17.0, released in September 2024, enables developers to target WebAssembly with a simple build tool configuration switch while preserving the complete semantics of the Scala.js language. Learn about the unique approach that maintains JavaScript interoperability features that Scala.js is renowned for, setting it apart from other languages targeting WebAssembly that typically compromise on JavaScript communication capabilities. Delve into the technical challenges faced during development and the innovative solutions designed to overcome them, including discussions on complex language semantics, low-level performance optimizations, large-scale redesign of the Intermediate Representation for lambdas, and new proposals to the WebAssembly specification. Gain insights from Sébastien Doeraene of Scala Center at EPFL as he shares the engineering decisions and architectural innovations that made this seamless WebAssembly integration possible while maintaining Scala.js's distinctive JavaScript interoperability strengths.