> just happens to interop with

It does not interop with JavaScript.

> and in some scenarios transpile down to JavaScript

It always transpiles to JavaScript and always runs as JavaScript. There is no such thing as a TypeScript runtime engine.

TypeScript is a superset of JavaScript. Therefore the OP's point is still valid. Any "mistakes" JavaScript might have made about having null AND undefined are also issues for TypeScript.

This does not necessarily invalidate your wider points, but just FYI:

> It does not interop with JavaScript.

Hm, this depends on your definition of "interop". My JavaScript and TypeScript are languages that exchange information. The execution model ultimately involves JavaScript when I use tsc, but ultimately it also includes an interpreter. My user-space syntax doesn't care.

> There is no such thing as a TypeScript runtime engine.

Not being glib, just a heaps up: https://github.com/denoland/deno

interesting thanks for the heads up - my assumption is though that this is just a wrapper over a V8 engine with typescript compilation on the fly?

Does that make it a TypeScript runtime or not?