find common names - design for performance

findCommonNames.js

const names = ['Huey', 'Dewey', 'Louie', 'Donald', 'Launchpad'];
const moreNames = ['Donald', 'Mickey', 'Minnie', 'Goofy', 'Chip', 'Dale'];

/**
 * Find common names in two arrays of names
 * @param names1
 * @param names2
 * @returns {[]} names contained in both arrays
 */
const findCommonNames = (names1, names2) => {
  const shared = [];
  const dict = new Map();
  // O(n)
  return names1.concat(names2).filter((name) => {
    if (dict.has(name)) {
      return true;
    } else {
      dict.set(name, 1);
      return false;
    }
  });
}

findCommonNames(names, moreNames);