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].

flattenArray.js

function flatten(array) {
  var idx,
      temp = [array],
      lastIdx = [-1],
      result = [];

  while(temp.length) {
    array = temp.pop();
    idx = lastIdx.pop() + 1;

    for(; idx < array.length; ++idx) {
      if (Array.isArray(array[idx])) {
        temp.push(array);
        lastIdx.push(idx);
        array = array[idx];
        idx = -1;
      } else {
        result.push(array[idx]);
      }
    }
  }

  return result;
}