Returns array which each of its elements appears only once

distinct.js

const arr = [1, 2, 2, 8, 5, 5, 3, 8, 3];

arr.sort().reduce((a, c) => {
  if (a.includes(c)) {
    return a;
  }

  a.push(c);
  return a;
}, []);

// -> [1, 2, 3, 5, 8]