Cast as a value of a tupe

tuple.ts

/**
 * Takes a string and returns it as an element of a tuple.
 *
 * In case of invalid value, returns default value if there is one, otherwise throw an error.
 */
export const castAsTupleOption = <Tuple extends readonly string[]>(
  options: Tuple,
  value: string | undefined,
  defaultValue?: Tuple[number],
): Tuple[number] => {
  if (value && options.includes(value)) {
    return value as Tuple[number];
  } else {
    if (defaultValue) return defaultValue;
    throw new Error(`The value doesn't match the expected values ${options.join(", ")}`);
  }
};

// ex


const colors = ["red", "green", "blue"] as const;

const myColor = castAsTupleOption(colors, "yellow", "red")

console.log("myColor", myColor)