Not possible to use string-valued enums in another enum's definition

[mgol]

🔎 Search Terms

Type is not assignable to type 'number' as required for computed enum member values

🕗 Version & Regression Information

• This changed between versions 4.9.5 and 5.0.4. Previously, this code was not flagged.

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.2.2#code/KYOwrgtgBAogjFA3gKClAglAvFA5O3AGmQF9lkBjAexAGcAXKUSW7JVWOYkgbnOegwATOzSYcA2gDp4U9N2RA

💻 Code

enum E1 {
  A = 'A',
}

const enums = {
  E1,
};

enum E2 {
  A = enums.E1.A,
}

🙁 Actual behavior

An error appears:

Type 'E' is not assignable to type 'number' as required for computed enum member values.

🙂 Expected behavior

No error should appear. Nothing in that code snippets expects numbers so this message is really confusing, especially that I'm just trying to use one string-valued enum in another one.

Additional information about the issue

Possibly related: #40793

In that issue, people are reporting similar problems, e.g.: #40793 (comment)

[MartinJohns]

You can just do: enum E2 { A = E1.A } The issue is not trying to use the value from another enum, but the indirection via a variable.

[mgol]

Yeah, I discovered that as well. In real code, both E1 & enums are bigger and a part of a separate package so I'd need to change its API to export the enums directly.

What's the reason for this behavior?

[RyanCavanaugh]

Emit can't rely on type information, and the emitter needs to know whether E2.A should be a string or numeric value (since string and numeric values have different enum emit), and the only way to do that is with type information.

[typescript-bot]

This issue has been marked as "Working as Intended" and has seen no recent activity. It has been automatically closed for house-keeping purposes.