Javascript Array Manipulation With Sets

[...new Set(arr)] // unique array
[...new Set(arr)].sort() // unique array sorted

// Union (deduped):
const union = (a1, a2) => [...new Set(a1.concat(a2))];

// Union arbitrary number of arrays:
[a1, a2, a3, ...].reduce((total, arr) => union(total, arr), []);

// Intersection (deduped):
const intersection = (a1, a2) => [...new Set(a1.filter(x => a2.includes(x)))];

// flatten array with any depth
const flat = (arr) => arr.reduce((a, value) => a.concat(
  Array.isArray(value) ? flat(value) : value
), []);