diff.js

// pinched (and tweaked) from https://gomakethings.com/getting-the-differences-between-two-objects-with-vanilla-js/

/*!
 * Find the differences between two objects and push to a new object
 * (c) 2019 Chris Ferdinandi & Jascha Brinkmann, MIT License, https://gomakethings.com & https://twitter.com/jaschaio
 * @param  {Object} obj1 The original object
 * @param  {Object} obj2 The object to compare against it
 * @return {Object}      An object of differences between the two
 */
var diff = function (obj1, obj2) {

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

  //
  // Variables
  //

  var diffs = {};
  var key;


  //
  // Methods
  //

  /**
   * 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
   */
  var arraysMatch = function (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
   */
  var compare = function (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] = 'Missing';
          return;
      }

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

      // If an object, compare recursively
      if (type1 === '[object Object]') {
          var objDiff = diff(item1, item2);
          if (Object.keys(objDiff).length > 1) {
              diffs[key] = objDiff;
          }
          return;
      }

      // Otherwise, just compare
      if (item1 === item2 ) {
          diffs[key] = `Identical to English: ${item2}`;
      }

  };


  //
  // Compare our objects
  //

  // 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;

};

module.exports = diff