How to represent nested array with typescript

Question

Say I have an array of strings like:

const a = ['foo', ['aa'], [['zzz',['bar']]]];
    
export const acceptsArray = (v: Array<any>) : string => {
   returns flattenDeep(v).join(' ');
};

besides using Array<any> how can I represent a nested array of strings?

Flavio Vilante · Answer 1 · 2022-01-06T12:18:13.023

13

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

edited Jan 06 '22 at 12:18

answered Jun 28 '19 at 11:53

Flavio Vilante

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does this go two levels deep? I am looking to represent an arbitrary level of nesting – Alexander Mills Jun 28 '19 at 18:57
1

yes it goes arbitrary level deep. – Flavio Vilante Jan 06 '22 at 12:23

score 6 · Accepted Answer · edited Jan 07 '22 at 03:27

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];
  }, []);
}

if it's always an array, seems like this would be more accurate? `export type NestedArray = Array | Array>;`, since T itself doesn't have to be an array here. — Alexander Mills, Dec 17 '21 at 04:30

How to represent nested array with typescript

2 Answers2