Typescript create string literal union type from array in object

Question

my goal is to create a string literal union type from an array in an object.

I know how to create a union type from an array, like so

const genderArr = ["female", "male"] as const;
type Gender = typeof genderArr[number]; // "female" | "male"

How can I achieve the same for an array inside of an object

const QuestionnaireOptions = {
    GENDER_OPTIONS: ["female", "male"],
    SIZE_OPTIONS: [
        "s",
        "m",
        "l",
    ],
};

type Gender = ??

I could not find any resource / similar stackoverflow post so far.

Thanks for your time!

Titian Cernicova-Dragomir · Accepted Answer · 2022-01-19 09:49:13Z

3

You can use a index access type to get a specific property of the container object:

const QuestionnaireOptions = {
    GENDER_OPTIONS: ["female", "male"],
    SIZE_OPTIONS: [
        "s",
        "m",
        "l",
    ],
} as const;

type Gender = typeof QuestionnaireOptions['GENDER_OPTIONS'][number]

Playground Link

edited Jan 19, 2022 at 9:49

answered Jan 19, 2022 at 9:44

Titian Cernicova-Dragomir

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2 Comments

captain-yossarian from Ukraine Over a year ago

I think worth adding docs link

oliveCshws Over a year ago

Missed to answer, thank you!!

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