return an array of unique elements from an arbitrary list of arrays

unicat.js

// why not let set and spread do all the work?
// arbitrary number of arrays, unique
function unicat(...arrays) {
  let collector = [];
  arrays.forEach((a) => {collector = collector.concat(a);});
  return Array.from(new Set(collector).values());
}

// O(n), i think, if concat() is implemented sanely.

let a = [1,2,3];
let b = [2,3,4];
let c = [4,5,6];
let u = unicat(a,b,c);
console.log(u); //=> 1,2,3,4,5,6