10. One Codebase, Three Runtimes

Coming soon

This chapter is an outline. The full draft ships in a follow-up PR.

What this chapter will cover

Scala 3 can target the JVM, JavaScript (via Scala.js), and native binaries (via Scala Native). Uni is designed so that a single piece of business logic compiles to all three. This chapter takes a working JVM service and shows the minimum changes needed to also ship it as a browser app and as a native binary.

Concepts introduced:

• sbt-crossproject: one build.sbt, three platforms.
• The .jvm, .js, and .native source folders and what belongs in each.
• Platform abstractions Uni gives you (HTTP, filesystem, timers) so your code stays identical.
• Things you cannot share: JVM-only file paths, browser-only DOM access, native-only syscalls — and how to isolate them.
• Building and distributing: a fat JAR, an optimized JS bundle, and a stripped native binary.

Reference you can read now

• Design Principles — Cross-Platform First
• HTTP Client — platform notes

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