How to build a type from enum values in TypeScript?

Question

Given the following:

enum FooKeys {   FOO = 'foo',   BAR = 'bar', } 

I'd like to make an interface like this one, but instead of defining keys by hand, build it out of enum's values.

interface Foo {   foo: string   bar: string } 

Is something like this possible with TypeScript?

Thanks!

Answer 1

Yes, you can use enum values as keys. And you can use a mapped type like the standard library's Record<K, V> to prevent repetition:

enum FooKeys {   FOO = 'foo',   BAR = 'bar', }  // probably all you need, but it's a type alias type FooType = Record<FooKeys, string>;  // if you need an interface instead you can do this interface FooInterface extends FooType {}; 

And you can verify that it works:

declare const foo: FooInterface; foo.foo; // okay foo[FooKeys.FOO]; // okay  foo.bar; // okay foo[FooKeys.BAR]; // okay  foo.baz; // error 

Does that work for you? Good luck!

Answer 2

@hackape 's solution is great, but I found minimal duplication extending his solution as below:

type ReverseMap<T extends Record<keyof T, any>> = {   [V in T[keyof T]]: {     [K in keyof T]: T[K] extends V ? K : never;   }[keyof T]; }  const Map = {   'FOO': "foo" as "foo",   'BAR': "bar" as "bar", }  const reverseMap: ReverseMap<typeof Map> = Object.entries(Map).reduce((rMap, [k, v]) => {   rMap[v] = k;   return rMap; }, {} as any);  export type Values = keyof typeof reverseMap; // 'foo' | 'bar'; 

ReverseMap implementation is well explained here