Vanilla Javascript FormData to object

form-data-to-object.js

/*
 * Converts FormData to object.
 *
 * @param {FormData} data
 *   To convert.
 * @return {string}
 *   FormData converted to object.
 */
function formDataToObject(data) {
  let value;
  let keys;
  let key;
  let part;
  let count;
  let object = {};
  for (let pair of data.entries()) {
    value = pair[1];
    keys = pair[0].split(/[\[\]]+/g);
    key = keys.shift();
    part = object;
    while (typeof key !== 'undefined') {
      if (key === '') {
        count = 0;
        while (part.hasOwnProperty(count)) {
          ++count;
        }
        key = count;
      }
      part[key] = keys.length ? {} : value;
      if (keys.length) {
        part = part[key];
      }
      key = keys.shift();
    }
  }
  return object;
}