typescript type from string values from an object

Question

The object with values as array of strings:

const STUFF = {
  abc: ["string_1", "string_2"],
  def: ["string_3", "string_4"],
  xyz: ["string_1", "string_2", "string_4"],
}

how to define a type that allows only values from these arrays?

type StuffStr = "string_1" | "string_2" | "string_3" | "string_4";

Answer 1

If you use a const assertion on STUFF, it becomes a matter of indexing typeof STUFF.

const STUFF = {
  abc: ["string_1", "string_2"],
  def: ["string_3", "string_4"],
  xyz: ["string_1", "string_2", "string_4"],
} as const;

type StuffStr = typeof STUFF[keyof typeof STUFF][number];
// type StuffStr = "string_1" | "string_2" | "string_3" | "string_4"

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