Extract different props from comparing two objects

extractDiffProps.js

const obj1 = {
  url: ['1', '2', '3'],
  fonts: {
    first: [1, 2],
    second: '2'
  },
  border: [1, 2, 3]
};

const obj2 = {
  url: ['1', '3', '4', '7'],
  fonts: {
    first: [5, 7, 2],
    second: '2'
  },
  border: [1, 2, 4, 6]
};

/**
 * Type checkers
 */
const isObject = col => !Array.isArray(col) && typeof col === 'object';
const isArray = col => Array.isArray(col);

const obj = isObject;
const arr = isArray;

/*
 * Iterators for objects/arrays
 */
const map = (col, fn) => (
  (obj(col) ? Object.keys(col) : col).map((key, i) => (
    fn(
      (obj(col) ? col[key] : key),
      (obj(col) ? key : i),
      col
    )
  ))
);

const filter = (col, fn) => {
  let res = [];
  (obj(col) ? Object.keys(col) : col).forEach((key, i) => (
    fn(key, i, col) && (
      res.push(obj(col) ? col[key] : key)
    )
  ))
  return res;
};

let res = {};
let parent = '';
const extractDiffProps = (previous, updated) => {
  map(previous, (elem, key) => {
    if (obj(elem)) {
      // Preserve the parent's key to create the returned object later
      parent = key;
      // If it finds an object call the fn again
      return extractDiffProps(elem, updated[key]);
    }

    // Clean the parent's name if no longer in that object
    if (updated[parent] !== previous[parent]) parent = '';

    if (arr(elem)) {
      // If array is inside an object: preserve parent's name as the key
      !!parent && (res[parent] = {
        [key]: updated[key].filter(i => !elem.includes(i))
      });

      // If array is not inside an object: key is equal to the currents element key
      !parent && (res[key] = updated[key].filter(i => !elem.includes(i)));
      return;
    }

    if (elem !== updated[key]) {
      // If object already exists: update it with a new prop
      res[parent] && (res[parent][key] = updated[key]);

      // If object doesn't exists: crete a new one
      !res[parent] && (res[parent] = {
        [key]: updated[key]
      })
    }
  });
  return res;
};

const res2 = extractDiffProps(obj1, obj2)
console.log(JSON.stringify(res2, null, 2))