Typescript: How can I define a type from an string array?

Question

Currently I do:

export const CValidEbookTypes = ['epub', 'mobi', 'pdf', 'azw3', 'txt', 'rtf'];
export type IEbookType = 'epub' | 'mobi' | 'pdf' | 'azw3' | 'txt' | 'rtf';

to have an array of valid book types and a typescript type, that defines them. This look quite redundant.

Is there a way to define the type using the array? My goal is obviously to avoid writing the book type twice. So any other solution would also be welcome.

You can use CValidEbookTypes[number], but you need to add as const after the array to infer the types as literals. — Ingo Bürk
– Ingo Bürk, Commented Aug 22, 2020 at 9:50

Johannes Reuter · Accepted Answer · 2020-08-22 09:55:18Z

2

By using as const, typescript infers the string literals as type for CValidEbookTypes. Then you can use typeof CValidEbookTypes[number]:

export const CValidEbookTypes = ['epub', 'mobi', 'pdf', 'azw3', 'txt', 'rtf'] as const;
export type IEbookType = typeof CValidEbookTypes[number];
// IEbookType will be "epub" | "mobi" | "pdf" | "azw3" | "txt" | "rtf"

answered Aug 22, 2020 at 9:55

Johannes Reuter

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