Issue
I work on a project with JS/TS mixed support
I’m looking for a way to reduce code duplication with JS string constants when wrapping them as Typescript types.
For example, I have constants for log type:
// logTypes.js
export const ERROR = 'error'
export const INFO = 'info'
Reexport them:
// constants.js
export * as LOG_TYPES from './logTypes.js'
And now I want to provide a TS type for this constants:
// types.d.ts
import { LOG_TYPES } from './constants'
export type LogType = ???
Obviously, I can declare the type like this and this will work:
// type LogType = "error" | "info", excellent
export type LogType = typeof LOG_TYPES.INFO | typeof LOG_TYPES.ERROR
But I think this is redundant, and also creates two points to be maintainable when somebody needs to extend the set of constants.
So, actually I would like to write something like this:
// Does not work as desired
// type LogType = any, meh
export type LogType = typeof LOG_TYPES[string]
I know there is a difference between types and values, but this specific part of import/export should be statically analyzable so I think there should be a way to do this I don’t know about
Solution
That is the idea indeed, but typeof LOG_TYPES cannot be indexed by string, but keyof typeof LOG_TYPES:
type LogType = typeof LOG_TYPES[keyof typeof LOG_TYPES]
// ^? "error" | "info"
Answered By – ghybs
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