Node.js can now execute TypeScript files

What are the recent improvements in node itself?

Last actually note-worthy improvement I heard of was properly supporting import/export (although do you still need to use the .mjs hack?), but I've been out of the loop here for sometime so would be nice to know what they've added since.

TypeScript never promised improving safety, maybe it’s a common misconception. But TypeScript has no runtime mode or information. You were always at the mercy of running and not ignoring the typechecker. Nothing stopped you from running ts-node or tsx on code with egregious type errors. TypeScript is more like a linter in that regard.

One of Typescript's design goals is that removing all type-related parts of the source text should yield a valid JavaScript file. A typescript compiler does not generate code (unlike, say, PureScript).

You can run a typechecker (such as tsc) that check various properties of your code statically, relying on the type information. It is then erased.

The same applies, say, to Python: type annotations are ignored at runtime. Somehow similarly, Java's type information is also partly erased in the bytecode; in particular, all the information about parametrized types. (This is to say nothing about actual machine code.)

Not needing a separate compile step just to run some script sounds great to me. I will run tsc if I want a type check.

I'm using tsx for a project to achieve the same effect. As you said, it saves you from having to set up a build/transpilation step, which is very useful for development. Tsx has a --watch feature built in as well, which allows me to run a server from the typescript source files and automatically restart on changes. Maybe with nodemon and this new node improvement this can now done without tsx.

To check types at runtime (if that can even be done in a useful way?) it would have to be built into v8, and I suppose that would be a whole rewrite.

Yes, it can't parse enums, for example.

Exactly! Type checking can be long and costly.

Yeah agreed - saying "node can execute typescript files" is a bit misleading. More accurate would be "node can find-and-replace type information with spaces from .ts files and try and executing them as if they were plain JavaScript"

I suspect this would only handle the most rudimentary and basic typescript files. Once you start using the type system more extensively I suspect this will blow-up in your face.

It's kinda a shame. What a missed opportunity to do it properly (rather than relying on third party plugins etc)

Edit: if you are just using typescript for type checking at build time (i.e. the most basic rudimentary typescript files) the sure fine this may help you. But typescript also generates JavaScript code for missing features e.g. proper class access modifiers, generics, interfaces, type aliases, enums, decorators etc etc. typescript generates JS code to handle all that, so you're going to have a bad time if node just replaces it with the space character at run time.

This has nothing to do with the "node world". Such an enormous feature would have to go into ECMAScript. Which is very, very unlikely to ever happen, they may as well design a new language. All those runtimes implement that spec, expecting them to write an extremely complex new feature that is more complicated than everything already implemented (especially with backwards compatibility) would be a bit much. It would also be way too troublesome.

TypeScript is for compile time checking of a language that was not designed to have them. Runtime types have very different requirements! It has to be in the language from the early design phase, otherwise it will just be a hack with many conditions, restrictions and holes.

I believe it would be too hard to keep up with pace of TypeScript development. We should probably at some point formally define the system and allow for alternative implementations outside of the control of Microsoft.