subSet

Checks if the first iterable is a subset of the second one, excluding duplicate values.

• Use the new Set() constructor to create a new Set object from each iterable.
• Use Array.prototype.every() and Set.prototype.has() to check that each value in the first iterable is contained in the second one.

const subSet = (a, b) => {
  const sA = new Set(a), sB = new Set(b);
  return [...sA].every(v => sB.has(v));
};

subSet(new Set([1, 2]), new Set([1, 2, 3, 4])); // true
subSet(new Set([1, 5]), new Set([1, 2, 3, 4])); // false