[2025-03-11] dev, typescript

Today’s announcement by Microsoft:

[…] we’ve begun work on a native port of the TypeScript compiler and tools. The native implementation will drastically improve editor startup, reduce most build times by 10×, and substantially reduce memory usage.

This blog post looks at some of the details behind the news.

Code bases: JavaScript vs. native  #

To avoid confusion, I’ll use these terms:

• JavaScript code base: the current code base of TypeScript – which is actually written in TypeScript.
• Native code base: the new code base. I’m using the term “native” because that’s what the TypeScript team does. The code is written in Go.

What’s the big deal?  #

Type checking is the one thing that external tools can’t do:

• Emitting .js has already become faster – thanks to native tools and type stripping.
• Emitting .d.ts has already become faster – thanks to native tools and isolated declarations.

Thus, type checking also becoming faster is great news.

The timeline  #

• The current version of TypeScript is 5.8.

• TypeScript 6 (JavaScript): The JavaScript code base will continue into the 6.x series, with 6.0 introducing some breaking changes to align with the native code base.

  • Original code name for TypeScript: Strada

• TypeScript 7 (native): Once the native code base has reached sufficient parity with the JavaScript code base, it’ll be released as TypeScript 7.0.

  • Code name for the native code base: Corsa.

Both code bases will co-exist for a long time.

What needs to be migrated?  #

It’s useful to note which parts of the TypeScript ecosystem are involved in the migration:

• The command line TypeScript compiler
• The TypeScript language server (which helps editors support TypeScript)
  • TypeScript predates (and inspired) the Language Server Protocol that is widely used now. The new language server will also use that protocol.
• Tools that uses the TypeScript code base
  • Interfacing with the Go code bases requires a completely new approach:
    • Fewer of the internals will be exposed.
    • Interactions now happen across processes.

When will the native version be ready for public consumption?  #

Rough predictions by Daniel Rosenwasser:

• Compiler without support for build mode (project references): end of 2025H1 (spring in USA)
• Compiler with build mode and language server: end of 2025.

When did the project start?  #

• First prototype by Anders Hejlsberg:
  • Started in August 2024
  • Scanner and parser took 1–1.5 months to write.
• Initial approach: write code manually.
• Later: tool that automatically ports TypeScript code to Go code.
  • Porting the code worked well (wit