Solution not sorted

[gtrman97]

freeCodeCamp.org

One solution is:

function uniteUnique(...arrays) {
  //make an array out of the given arrays and flatten it (using the spread operator)
  const flatArray = [].concat(...arrays);

  // create a Set which clears any duplicates since it's a regular set and not a multiset
  return [...new Set(flatArray)];
}

// test here
uniteUnique([1, 3, 2], [5, 2, 1, 4], [2, 1]);

But I tried this and it’s not sorted.

function uniteUnique(...arr) {
  const flatArray = [].concat(...arr);
  console.log(flatArray)
  console.log([...new Set(flatArray)]);
  return [...new Set(flatArray)];
}

uniteUnique([1, 3, 2], [5, 2, 1, 4], [2, 1]);

[sanity]

It isn’t sorted in numerical order, but it is sorted by the order in which each number appears in the original arrays, as per description.

[isiagi]

Yes, the array is not sorted because at first there is a concatenation of arrays into one array and result is

[1, 3, 2, 5, 2, 1, 4, 2, 1]

And then we are calling the new Set() method which remove all duplicate occurrences but considering the first occurrence to be valid and the others duplicate occurrences of the same element will be removed thus NOT SORTING

[1, 3, 2, 5, 4]

The result is not sorted because each number is put from the first occurrence point (index) and the other similar number(s) at a later point (index) are removed.
We can use the sort method to sort the result if need be.