typescript-is VS class-validator

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

In 14.03.2022 I asked a question1 in class-validator repo about throwing an error when a user sends multiple data while we're gonna allow them to only send one of them.

You can learn more from the documentation here.

This is the request body when creating a new task. The IsString decorator provided by class-validator rejects all types other than strings, including undefined or null. The task name value object does not consider the possibility of values other than strings.

In this class, we are using the famous class-validator to decorate our request parameters. This way it is more clear how we are going to use our request object and everything.

We add validation using https://github.com/typestack/class-validator.

I will make sure we get this documented.

Also OP can check out class-transformer + class-validator if he want to properly instantiate objects and validate them with precise and verbose output of potential format errors. OP can even go the god tier way by setting up a custom RxJS operator that does that for him easily.

Start by installing the class-transformer and class-validator packages for dto validation (see more in the docs), sharp for image optimization, and the S3 client packages.

The description of the request body model in NestJS is similar to the description of Ditsmod models, but NestJS uses decorators provided by the utility class-validator. In NestJS, it is customary to name the request body model with the ending *Dto (this is an abbreviation of Data transfer object):

You could use Zod or Superstruct to validate the types of values, or use typestack/class-validator if it makes sense.