JavaScript. How to Compare Input Arrays

Question

I\'m stuck with this problem for 3 days now... Someone please help me.

Challenge 5
Construct a function intersection

Answer 1

Reduce the arrays to a Map of counts, with the value as key. Spread the Map to entries. Use Array.filter() on the Map's entries to remove all entries, which value is not equal to the arrayOfArrays lenth. Extract the original number from the entries using Array.map():

function intersection(arrayOfArrays) {
  return [...arrayOfArrays.reduce((r, s) => {
    s.forEach((n) => r.set(n, (r.get(n) || 0) + 1));
    
    return r;
  }, new Map())]
  .filter(([k, v]) => v === arrayOfArrays.length)
  .map(([k]) => k);
}

console.log(intersection([[5, 10, 15, 20], [15, 88, 1, 5, 7], [1, 10, 15, 5, 20]]));