how to flatten a nested array using recursion in javascript

Question

I am trying to flatten a nested array contained in array variable. Everything looks fine in the code but still not working. Please help me what's wrong with my code. According to me this code should return a flatten array like [1,2,3,4].

var array = [1,[2],[3,[[4]]]];

function flatten(array){

        return array.map(function(currentElement){

            if(Array.isArray(currentElement)){
                return flatten(currentElement);
            }else{
                return currentElement;
            }
        });
}

console.log(flatten(array)); // [1,[2],[3,[[4]]]]

// expected result => [1,2,3,4]

what about calling simply array.toString() – M14 Jun 04 '18 at 10:48 — M14, Jun 04 '18 at 10:48

Ankit Agarwal · Answer 1 · 2018-06-04T11:17:47.623

1

Just use toString()

var array = [1,[2],[3,[[4]]]];
array = array.toString();
array = array.split(',');
console.log(array);

edited Jun 04 '18 at 11:17

answered Jun 04 '18 at 10:49

Ankit Agarwal

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nice solution... :) – Ankur Shah Jun 04 '18 at 10:52
@AnkurShah welcome – Ankit Agarwal Jun 04 '18 at 10:53
But I need to flatten this array using Recursion. is my code wrong? – Gopendra Jun 04 '18 at 11:14

ZER0 · Answer 2 · 2018-06-04T11:23:33.760

1

You can use a combo of reduce and concat for this purpose, since flat is not implemented yet in the majority of the browsers.

const flatten = array => 
  array.reduce((r, v) => r.concat(Array.isArray(v) ? flatten(v) : v), []);


console.log(flatten([1,[2],[3,[[4]]]])) // [1, 2, 3, 4]

edited Jun 04 '18 at 11:23

answered Jun 04 '18 at 11:16

ZER0

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thanks a lot. it was helpful. – Gopendra Jun 04 '18 at 11:28
but still could not find why my code is not working. – Gopendra Jun 04 '18 at 11:50
1

Because you don't use `concat`, that's the key method. And, you're using `map`, so you can't really flatten with `map` since it returns always an array (of array, in your case). – ZER0 Jun 04 '18 at 12:41

how to flatten a nested array using recursion in javascript

2 Answers2