function steamrollArray(val,flatArr=[]) {
  val.forEach(item => {
    if ( Array.isArray(item)) 
 steamrollArray(item, flatArr);
    else flatArr.push(item);
  return flatArr;
steamrollArray([1, [2], [3, [[4]]]]);

Not sure what the problem is here. I keep getting the error // running tests Your solution should not use the Array.prototype.flat() or Array.prototype.flatMap() methods. // tests completed

Can someone help me with this please?

I thought that bug was fixed. Does it work if you change flatArr to bananas?

oh my god… you are totally right. It works. Thank you so much

: ) This bug is bananas.