Returns every element that exists in any of the two arrays once.
Create a Set with all values of a and b and convert to an array.
const union = (a, b) => Array.from(new Set([...a, ...b]));
union([1, 2, 3], [4, 3, 2]); // [1,2,3,4]
Returns every element that exists in any of the two arrays once, after applying the provided function to each array element of both.
Create a Set by applying all fn to all values of a. Create a Set from a and all elements in b whose value, after applying fn does not match a value in the previously created set. Return the last set converted to an array.
const unionBy = (a, b, fn) => { - const s = new Set(a.map(v => fn(v))); + const s = new Set(a.map(fn)); return Array.from(new Set([...a, ...b.filter(x => !s.has(fn(x)))])); };
unionBy([2.1], [1.2, 2.3], Math.floor); // [2.1, 1.2]