flatten

Write a recursive function called flatten which accepts an array of arrays and returns a new array with all of the values flattened

Examples

flatten([1, 2, 3, [4, 5] ]) // [1, 2, 3, 4, 5]
flatten([1, [2, [3, 4], [[5]]]]) // [1, 2, 3, 4, 5]
flatten([[1],[2],[3]]) // [1,2,3]
flatten([[[[1], [[[2]]], [[[[[[[3]]]]]]]]]]) // [1,2,3

Solution #1

function flatten(arr) {
  if (arr.length < 1) return arr;
  if (Array.isArray(arr[0])) return flatten(arr[0]).concat(flatten(arr.slice(1)));
  return [arr[0]].concat(flatten(arr.slice(1)));
}

Solution #2

function flatten(oldArr){
  var newArr = []
    for(var i = 0; i < oldArr.length; i++){
      if(Array.isArray(oldArr[i])){
            newArr = newArr.concat(flatten(oldArr[i]))
      } else {
            newArr.push(oldArr[i])
      }
  } 
  return newArr;
}