Question

17

Typescript object: How do I restrict the keys to specific strings?

rated 0 times [ 19] [ 2] / answers: 1 / hits: 20791 / 7 Years ago, sun, november 12, 2017, 12:00:00

I want to create an object of type Partial, where the keys will be some combination of 'a', 'b', or 'c'. It will not have all 3 keys (edit: but it will at least have one). How do I enforce this in Typescript? Here's more details:

// I have this:

type Keys = 'a' | 'b' | 'c'



// What i want to compile:

let partial: Partial = {'a': true}

let anotherPartial: Partial = {'b': true, 'c': false}



// This requires every key:

type Partial = {

  [key in Keys]: boolean;

}



// This throws Typescript errors, says keys must be strings:

interface Partial = {

  [key: Keys]: boolean;

}

The two methods I've tried above (using mapped types and interfaces) don't achieve what I want. Can anyone help here?

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ansleyk

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2 Years ago

answered 7 Years ago amari · Accepted Answer

You can use the ? to make the keys optional, so

interface Partial {

   a?: boolean;

   b?: boolean;

   c?: boolean;

}

Or, you can do this:

type Keys = a | b | c;



type Test = {

    [K in Keys]?: boolean

}