I am a little surprised that they rewrote the compiler in Go instead of just compiling the existing compiler to WASM. The linked announcement does not talk about a WASM alternative at all (rewriting a compiler is a risky move!). Does anybody know what the rationale was to do a full rewrite? The article really emphasizes speed, but not much else. Was it Go's concurrency affordances that made the switch worthwhile?

The compiler was written in TS; it wouldn't make much sense to compile TS to Wasm, only to have that same code run in the same interpreter as the JS code.

And yes, threading was a big part of it. See also: https://devblogs.microsoft.com/typescript/typescript-native-...