typescript-is VS TypeScript

I'll throw https://github.com/woutervh-/typescript-is in the mix as well.

I'm a fan of typescript-is. Provides both compile time and run time validations

For what it's worth, thanks to TypeScript transformers (a feature baked into the compiler), one can create a transformer library that verifies an object is valid for any TypeScript type and conveys that information to the typechecker. And indeed, it's already been made. It allows to parse unknown into a given T. This is nice, because one can generate a JSON schema out of a TS type, for other languages/codebases to integrate safely.

But to make it worth the comment, I’ll point people to typescript-is which uses transformations at compile-time to generate run-time type checking code.

Then there's also typescript-is, which is pretty neat because it converts actual compile-time type definitions to runtime type checks, so it doesn't require changing the type definitions.

typescript-is. This uses a compile-time transformer to generate code for type-checking. You'll need to use ttypescript instead of typescript to compile your code (I recommend setting this up with ts-patch). It won't work if your build pipeline is actually using something like esbuild or Babel to transpile TS->JS.

If you're not using a bunch of generics, check out typescript-is [1]. It takes little work to get it setup, but it generates run time type checks for you. I understand why typescript decided to not add this functionality to the core of the language, but it's starting to feel like the largest missing piece of typescript is a built-in way to generate run-time type-checks for user-defined types from just the type definition.

The happy medium we've found with that module is using the runtime type-check on anything "unsafe" to bless the result using typescript-is's equals functionality, but still allowing programmers to use casting with a comment justifying its necessity. For us our list of unsafe is results pulled from the db, anything parsed from JSON, and incoming request bodies (which can be a special case of parsing from JSON, but not always).

[1]: https://github.com/woutervh-/typescript-is

While we were fighting against the modules, we forgot one small detail - their built-in typings. Esbuild can't do this at all yet. Unbelievable, but the tsc, native TS compiler, also does not provide a typings concat feature. Got around this problem: we've introduced [a utility to combine typings](tsc-dts-fix of zx own code, and applied some monkey patches for external libdefs squashed via dts-bundle-generator.

Regular expressions are part of the language, so it's not so unreasonable that TypeScript should parse them and take their semantics into account. Indeed, TypeScript 5.5 will include [new support for syntax checking of regular expressions](https://github.com/microsoft/TypeScript/pull/55600), and presumably they'll eventually be able to solve the problem the GP highlighted on top of those foundations.

Dedicated syntax for creating unique subsets of a type that denote a particular refinement is a longstanding ask[2] - and very useful, we've experimented with implementations.[3]

I don't think it has any relation to runtime type checking at all. It's refinement types, [4] or newtypes[5] depending on the details and how you shape it.

[1] https://github.com/microsoft/TypeScript/blob/main/src/compil...

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