Typescript Union Array using String Enum for Key Names

Question

Is there a way to short form this statement:

Array<{ [enum.example1]: Example } | { [enum.example2]: Example } | ...>
// or equivalent
({ [enum.example1]: Example } | { [enum.example2]: Example } | ...)[];

So it is more succinct like { [key: string]: Example }, but uses a string enum to restrict the possible keys:

For example, these don't appear to work:

{ [enum]: Example }[];
// or
{ [key: enum]: Example }[];

Martin Parenteau · Accepted Answer · 2019-01-27 23:25:47Z

1

You can use the same syntax as for a limited set of string literals:

{ [key in MyEnum]?: Example }[]

See this stackblitz for a demo.

edited Jan 27, 2019 at 23:25

answered Jan 27, 2019 at 23:17

Martin Parenteau

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3 Comments

mtpultz Over a year ago

Is it possible do something similar with an interface like in this example stackblitz.com/edit/angular-gmq9qp?embed=1&file=src/app/…? Seems to indicate an error, and if I change the keys in test to something outside the enum it seems to accept it.

Martin Parenteau Over a year ago

According to the error message, it appears to be disallowed in an interface declaration. I don't know if there is a workaround in that case.

mtpultz Over a year ago

Thanks, you're right. Looks like it isn't. You need to use an alias like export type Alias = { [key in Example]: string; }, or wait for github.com/Microsoft/TypeScript/pull/26797.

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