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!

Answer 1

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