objectDiff.js

const objectDiff = (obj1, obj2) => {

  // Make sure an object to compare is provided
  if (!obj2 || Object.prototype.toString.call(obj2) !== '[object Object]') {
      return obj1;
  }

  let diffs = {};
  let key;

  /**
   * Check if two arrays are equal
   * @param  {Array}   arr1 The first array
   * @param  {Array}   arr2 The second array
   * @return {Boolean}      If true, both arrays are equal
   */
  const arraysMatch = (arr1, arr2) => {

      // Check if the arrays are the same length
      if (arr1.length !== arr2.length) return false;

      // Check if all items exist and are in the same order
      for (var i = 0; i < arr1.length; i++) {
          if (arr1[i] !== arr2[i]) return false;
      }

      // Otherwise, return true
      return true;

  };

  /**
   * Compare two items and push non-matches to object
   * @param  {*}      item1 The first item
   * @param  {*}      item2 The second item
   * @param  {String} key   The key in our object
   */
  const compare = (item1, item2, key) => {

      // Get the object type
      var type1 = Object.prototype.toString.call(item1);
      var type2 = Object.prototype.toString.call(item2);

      // If type2 is undefined it has been removed
      if (type2 === '[object Undefined]') {
          diffs[key] = null;
          return;
      }

      // If items are different types
      if (type1 !== type2) {
          diffs[key] = item2;
          return;
      }

      // If an object, compare recursively
      if (type1 === '[object Object]') {
          const objDiff = objectDiff(item1, item2);
          if (Object.keys(objDiff).length > 0) {
              diffs[key] = objDiff;
          }
          return;
      }

      // If an array, compare
      if (type1 === '[object Array]') {
          if (!arraysMatch(item1, item2)) {
              diffs[key] = item2;
          }
          return;
      }

      // Else if it's a function, convert to a string and compare
      // Otherwise, just compare
      if (type1 === '[object Function]') {
          if (item1.toString() !== item2.toString()) {
              diffs[key] = item2;
          }
      } else {
          if (item1 !== item2 ) {
              diffs[key] = item2;
          }
      }

  };

  // Loop through the first object
  for (key in obj1) {
      if (obj1.hasOwnProperty(key)) {
          compare(obj1[key], obj2[key], key);
      }
  }

  // Loop through the second object and find missing items
  for (key in obj2) {
      if (obj2.hasOwnProperty(key)) {
          if (!obj1[key] && obj1[key] !== obj2[key] ) {
              diffs[key] = obj2[key];
          }
      }
  }

  // Return the object of differences
  return diffs;

};