How to represent nested array with typescript

SOLUTION

Note only works on Typescript version 3.7+

type A = 'foo' | 'aa' | 'zzz' | 'bar' | A[]

const a:A = ['foo', ['aa'], [['zzz',['bar']]]];

export const acceptsArray = (v: Array<A>) : string => {
   returns flattenDeep(v).join(' ');
};

Thank you

Please check this utility function I wrote earlier.

// NestedArray<T> represents T or Array of T or Array of Array of T .....
// let nestedNumbers: NestedArray<number> = [[[[[1]]]]];
export type NestedArray<T> = Array<T> | Array<NestedArray<T>>;

// Able to flatten deeply nested array
// flattenArray(nestedNumbers) should produce => [1] : Array<number>
export const flattenArray = <T>(arr: NestedArray<T>): Array<T> => {
  if (!Array.isArray(arr)) return arr ? [arr] : [];

  return arr.reduce<Array<T>>((acc: Array<T>, item: NestedArray<T>) => {
    if (Array.isArray(item)) {
      return [...acc, ...flattenArray(item)];
    }
    return [...acc, item];
  }, []);
}