Removes all duplicates from an array

removeDuplicates.js

/**
 * Removes all duplicates from an array (retaining only the first
 * occurrence of each array element).  This function modifies the
 * array in place and doesn't change the order of the non-duplicate items.
 *
 * For objects, duplicates are identified as having the same unique ID as
 * defined by {@link goog.getUid}.
 *
 * Runtime: N,
 * Worstcase space: 2N (no dupes)
 *
 * @param {goog.array.ArrayLike} arr The array from which to remove duplicates.
 * @param {Array=} opt_rv An optional array in which to return the results,
 *     instead of performing the removal inplace.  If specified, the original
 *     array will remain unchanged.
 */
goog.array.removeDuplicates = function(arr, opt_rv) {
  var returnArray = opt_rv || arr;

  var seen = {}, cursorInsert = 0, cursorRead = 0;
  while (cursorRead < arr.length) {
    var current = arr[cursorRead++];

    // Prefix each type with a single character representing the type to
    // prevent conflicting keys (e.g. true and 'true').
    var key = goog.isObject(current) ?
        'o' + goog.getUid(current) :
        (typeof current).charAt(0) + current;

    if (!Object.prototype.hasOwnProperty.call(seen, key)) {
      seen[key] = true;
      returnArray[cursorInsert++] = current;
    }
  }
  returnArray.length = cursorInsert;
};