Deriving union type in Typescript from values within a module or object

Question

Deriving union type in Typescript from values within a module or object

I'm trying to find a method similar to keyof typeof myModule in typescript. However, instead of a union of key strings, I need a union of the value types.

I have a module with an increasing number of exports -

myModule.ts:

export const Thing1;
export const Thing2;
export const Thing3;
// ... many more things!

This module is imported elsewhere, and I want to create a union type that is Thing1 | Thing2 | Thing3 | ..., without having to do it manually.

anotherModule.ts:

import * as things from './myModule';

type AnyThingKey = keyof typeof things;

function useThings(thing: /* AnyThing - this is where/how I'd use the union type */) {
    // ... do things ...
}

Is there a standard way to achieve this?

typescript

Answer 1

Answer №1

You're on the right track towards finding the solution.

It looks like your anotherModule.ts file should resemble this:

import * as data from './myModule';

type AnyDataKey = typeof data[keyof typeof data];

function useData(dataItem: AnyDataKey) {
  // ... implement functionality here ...
}

useData("data1"); // This is fine
useData("bar");   // This will trigger a compiler error

Answer 2

You're on the right track towards finding the solution.

It looks like your anotherModule.ts file should resemble this:

import * as data from './myModule';

type AnyDataKey = typeof data[keyof typeof data];

function useData(dataItem: AnyDataKey) {
  // ... implement functionality here ...
}

useData("data1"); // This is fine
useData("bar");   // This will trigger a compiler error

Deriving union type in Typescript from values within a module or object

Answer №1

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