Flattens an array of integers like [[1,2,[3]],4] -> [1,2,3,4].

Utils.js

/**
 * Flattens an array of integers like [[1,2,[3]],4] -> [1,2,3,4].
 * @param {array} inputArray The array of integers and/or array of integers.
 * @returns {array} Flatten array.
 */
function arrayFlatten(inputArray) {
  const arrayOfStrings = inputArray.join(',').split(',');
  return arrayOfStrings.map(x => parseInt(x, 10));
}
// test arrayFlatten
console.log(arrayFlatten([1, 5, [6, [7, 9, 8]], [4, 6, 8, [3, 5, 8, 9, [2, 4, 6]]]]));