Determine if an object in TypeScript generics includes a specific value

I have been working on a method to verify if a value retrieved from the database matches an enum. At first, I aimed to create a generic TypeGuard, but then I thought it would be beneficial to have a function that not only checks the value against the enum but also handles both scenarios. Unfortunately, TypeScript does not allow using `` in the generics declaration. Instead, I opted to compare the value with an object, a more abstract approach that I find quite practical.

typeGuard<E extends Object>(value: string): value is E {
  return Object.values(E).includes(value);
}

Upon realizing that passing E to Object.values() is invalid since E is a type, not an object, I encountered a roadblock. One workaround could be passing the object as another argument, but that seems cumbersome as I won't be utilizing the object in any other way. The same issue arises if I only need it as a function, not a type guard.

typeGuard<E extends Object>(values: string): boolean {
  return Object.keys(E).includes()
}

In summary, I am seeking a method to validate if a given value corresponds to a value within an object solely based on the object's type, without referencing the object itself. Is there a solution to achieve this?

Answer №1

Unfortunately, typescript compilers do not pass any type information into runtime.

While there are some ways to pass static types into runtime using transformers, it is unlikely to work with passing types into generic call functions.


If you want to ensure that an object matches a specific (deep) type correctly, it is recommended to use Zod or a newer tool like . These tools may involve some boilerplate code (especially Zod), but they help ensure that objects are of the proper type.
ArkType, in particular, has simpler boilerplate and makes it easy to infer TypeScript type definitions from validator definitions, so I suggest checking that out.

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