Array to map

array-to-map.js

function flatten(arr) {
  return [].concat(...arr);
}

function combine(keys, values) {
  return keys.reduce((acc, key, i) =>
    ({ ...acc, [key]: values[i] || null }), {}
  );
}

const processedDates = [
  [1, 2],
  // [3, 4],
  [5, 6]
];

const keys = [
  "freeMonthStart", "freeMonthEnd",
  "freeMonth2Start", "freeMonth2End",
  "freeMonth3Strat", "freeMonth3End"
];

const dates = flatten(processedDates);

result = combine(keys, dates);

console.log(result);