flatten_array.js

// After reviewing the exercise again, I thought this revision is much cleaner and wanted to take out the extra function to not overcomplicate it

function flatten_array(input){
  var result = [];
  for (var i = 0; i < input.length; i++){
    var flattened = input[i];
    result = result.concat(Array.isArray(flattened) ? flatten_array(flattened) : flattened);
  }
  return result;
}

console.log(flatten_array([[1,2,[3]],4]));

console.log(flatten_array([[1,2,[3]],4, [5, 6, 8, [9, 10, [11, [12, [13, [14, 15, [16, 105, [109302940, 31409024, [9594590850]]]]]]]]]]));