type guards for classes

[insomnimus]

Is it possible to generate type guards for classes as well?

I'm currently facing a problem where I need to declare what used to be an interface as a class due to @nestjs/swagger requiring classes for the decorators to work.
ts-auto-guard does not seem to generate any type guard for classes. Is this intended behaviour?

[rhys-vdw]

@insomnimus you can do: myInstance instanceof SomeClass in JS. You don't need any codegen.

[insomnimus]

I'm instantiating this class from JSON. I need to define the request body an endpoint expects, and since decorators don't work on interfaces (at least the ones I'm using don't), nestjs/swagger requires me to use classes for the DTO.

If there isn't a technical blocker for this feature, I think it would be nice to have the option to be able to generate guards for classes, as the generated code should be exactly the same.

[rhys-vdw]

Your scenario doesn't make sense to me. A class is based on prototype chain. There is no such thing as instantiating a class from JSON (at least not standard JSON), because JSON can't set __proto__. Therefore the result will always be false unless you want it to lie to you. Objects can only fulfill interfaces/types, not classes, so probably you would need to do something like this:

/** @see {isFoo} ts-auto-guard:type-guard */
interface Foo {
  x: number;
  y: string;
}

class FooClass implements Foo {}

let payload = await getMyPayload()
if (!isFoo(payload)) {
  throw new Error("That isn't foo!");
}

let new fooClass = new Foo();
Object.assign(fooClass, payload);

[rhys-vdw]

btw this project is basically dead, maybe you could try asking over at https://typia.io/