Write some code, that will flatten an array of arbitrarily nested arrays of integers into a flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4].

flatten.js

let array =  [[1,2,[3],4],[5, 6,[7]]];
let newArray = flatten(array);

function flatten(array) {
  if (!array || !array.length) return [];

  let stack = [],
      indexes = [],
      currentIdx = 0,
      results = [];
  
  do {
    if (!array[currentIdx]) {
      array = stack.pop();
      currentIdx = indexes.pop() + 1;
    } else if (Array.isArray(array[currentIdx])) {
      stack.push(array);
      indexes.push(currentIdx);
      array = array[currentIdx];
      currentIdx = 0;
    } else {
      results.push(array[currentIdx]);
      currentIdx++
    }
  } while (array);
  
  return results;
}