An efficient way to find duplicates in JavaScript - specifically the duplicate objects of two arrays. Time: O(m) | Space: O(n)

find-duplicate-objects.js

/**
 * -----------------------------------------------
 * Function (findDuplicates)
 * -----------------------------------------------
 * @desc Find the duplicate objects in two arrays. With m representing
 *   the length of the longest array and n the length of both arrays
 *   combined, this function operates in - Time: O(m) | Space: O(n).
 * @param {Array<Object>} arr1 - The first array.
 * @param {Array<Object>} arr2 - The second array.
 * @return {Array<Object>} The duplicates.
 */
function findDuplicates(arr1, arr2) {

  /** @type {Array<Object>} */
  var maxArr;
  /** @type {Array<Object>} */
  var minArr;
  /** @type {number} */
  var maxLen;
  /** @type {number} */
  var minLen;
  /** @type {Object<string, number>} */
  var hashMap;
  /** @type {Array<Object>} */
  var duplicates;
  /** @type {number} */
  var i;
  /** @type {string} */
  var propString;

  maxArr = (arr1.length > arr2.length) ? arr1 : arr2;
  minArr = (arr1.length < arr2.length) ? arr1 : arr2;
  maxLen = maxArr.length;
  minLen = minArr.length;
  hashMap = {};
  duplicates = [];

  i = maxLen;
  while (i--) {

    // Add maxArr item to hash map or duplicates
    propString = makePropString( maxArr[i] );
    if ( hashMap.hasOwnProperty(propString) ) {
      duplicates.push( maxArr[i] );
      ++hashMap[ propString ];
    }
    else {
      hashMap[ propString ] = 1;
    }

    // Add minArr item to hash map or duplicates
    if (i < minLen) {
      propString = makePropString( minArr[i] );
      if ( hashMap.hasOwnProperty(propString) ) {
        duplicates.push( minArr[i] );
        ++hashMap[ propString ];
      }
      else {
        hashMap[ propString ] = 1;
      }
    }

  }

  return duplicates;
}

/**
 * -----------------------------------------------
 * Function (makePropString)
 * -----------------------------------------------
 * @desc Make a string of the object's unique properties.
 * @param {Object<string, *>} obj - The object.
 * @return {string} The property string.
 */
function makePropString(obj) {

  /** @type {string} */
  var prop;
  /** @type {string} */
  var propString;

  propString = '';

  for (prop in obj) {
    if ( obj.hasOwnProperty(prop) ) {
      propString += prop + String( obj[ prop ] );
    }
  }

  return propString;
}