FR: Add an option for generating string enum.

[Rin0107]

TL;DR

I propose an option that generate string enum (instead of numeric enum).

For example, the current enum generation looks like this:

enum Role {
  UNSPECIFIED = 0,
  ADMIN = 1,
  INTERNAL_ADMIN = 2,
  CONSUMER = 3
}

With the proposed string enum:

enum Role {
  UNSPECIFIED = ‘UNSPECIFIED’,
  INTERNAL_ADMIN = ‘INTERNAL_ADMIN’
  CONSUMER = ‘CONSUMER’
}

Why

Numeric enum in TS has a problem. It is type unsafe.
It is allowed below access.

enum Role {
  UNSPECIFIED = 0,
  ADMIN = 1,
  INTERNAL_ADMIN = 2,
  CONSUMER = 3
}

console.log(Role[4]) // It is expected compile error but…
=> undefiend

String enums can check it and occur compile error.

Then, in below use-case, only-numeric-enums-generate cause a problem.
I face it in a situation like that I generated ts code in BFF (Backend for Frontend) from Backend protobuf.
ClientSide and Backend expect string (e.g ‘ADMIN’), but BFF has only numeric enum, so BFF has to re-defien string enum by myself.

enum RoleByMyself {
  UNSPECIFIED = ‘UNSPECIFIED’,
  INTERNAL_ADMIN = ‘INTERNAL_ADMIN’
  CONSUMER = ‘CONSUMER’
}

console.log(RoleByMyself[‘INTERNAL_ADMIN’])
=> ‘INTERNAL_ADMIN’
console.log(RoleByMyself[‘foo’]) // As expected, compile error 

For reference, stephenh/ts-proto has this option stringEnums=true.

Thanks for reading!

[timostamm]

Hey Rin,

regarding type-safety: TypeScript enums provide an index signature that behaves like any other index signature. For example:

const arr: string[] = [];
const val: string = arr[1]; // actually undefined

You can configure the behavior with the compiler option noUncheckedIndexedAccess. TypeScript are certainly not perfect, but I'm not sure this specific issue is the most problematic, or that it warrants switching to string enums - which don't even provide a mapping from numeric values at all.

Regarding a BFF, can you provide more details on the situation? What format exactly are BFF and F using? I suspect that there's already a solution.

[Rin0107]

Thanks for replying!

Ok, I got your description of behaves about index signature.
For notes, this post speaks for my opinion.

And I sincerely appreciate your kindness in asking my situation.
Tomorrow, I will provide a more detailed explanation of it in my next comment.

[timostamm]

For notes, this post speaks for my opinion.

I agree with the bundle size concerns, but the type-safety issue has been addressed with TypeScript 5. It will raise an error at compile time for the example, with standard compiler settings.

[Rin0107]

First, I'm sorry that I misunderstood that string enum will help my situation.
So, I close this issue.

Thank you for taking the time.