Flatten & unflatten

flatten-un.js

function unflatten(data) {
  if (Object(data) !== data || Array.isArray(data)) {
    return data;
  }
  let regex = /\%?([^%\[\]]+)|\[(\d+)\]/g,
    resultholder = {};
  for (let p in data) {
    if (data[p]) {
      let cur = resultholder,
        prop = '',
        m;
      /*jshint -W084*/
      while (m = regex.exec(p)) {
        cur = cur[prop] || (cur[prop] = (m[2] ? [] : {}));
        prop = m[2] || m[1];
      }
      cur[prop] = data[p];
    }
  }
  return resultholder[''] || resultholder;
}

function flatten(data) {
  let result = {};

  function recurse(cur, prop) {
    if (Object(cur) !== cur) {
      result[prop] = cur;
    } else if (Array.isArray(cur)) {
      for (let i = 0, l = cur.length; i < l; i++) {
        recurse(cur[i], prop + '[' + i + ']');
      }
      if (!cur.length) {
        result[prop] = [];
      }
    } else {
      let isEmpty = true;
      for (let p in cur) {
        if (cur[p]) {
          isEmpty = false;
          recurse(cur[p], prop ? prop + '%' + p : p);
        }
      }
      if (isEmpty && prop) {
        result[prop] = {};
      }
    }
  }
  recurse(data, '');
  Object.keys(result).map((k) => {
    if ((typeof result[k] === 'object') && (result[k] !== null)) {
      delete result[k];
    }
  });
  return result;
}