Typescript one of array

function stringLiterals<T extends string>(...args: T[]): T[] { return args; }
type ElementType<T extends ReadonlyArray<unknown>> = T extends ReadonlyArray<infer ElementType> ? ElementType : never;

const values = stringLiterals('A', 'B');
type Foo = ElementType<typeof values>;

const v1: Foo = 'A' // This should work
const v2: Foo = 'D' // This should give me an error since 'D' doesn't exist in values

Source: github.com

Typescript one of the array items

const animals = ['cat', 'dog', 'mouse'] as const
type Animal = typeof animals[number]

// type Animal = 'cat' | 'dog' | 'mouse'

Source: steveholgado.com

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