A function which takes a string and returns a new one with only unique characters.

uniqChars.js

/**
 * Gets a copy of the string with all duplicate characters removed.
 * @name uniqChars
 * @function
 * @param {string} str
 *   Input string which will be duplicated and whose duplicate characters will
 *   be removed.
 * @returns {string}
 *   A copy of `str` with all duplicate characters removed.
 */
function uniqChars(str) {
  return str.replace(/[\s\S](?=([\s\S]+))/g, function(c, s) {
    return s.indexOf(c) + 1 ? '' : c;
  });
}