How to get the unique value of 2 arrays

Question

I need compare 2 arrays, 'a' and 'b' and to rescue the field that is not in 'a' array and save it in 'c' array

something like this:

let a = ['1', '2', '3']
let b = ['1', '2']

let c = a.compare(b)

c = ['3']

Answer 1

Make a Set (contains unique values) and filter it to check that the values don't exist in either one of the arrays

let a = ['1', '2', '3']
let b = ['1', '2']

let co = [...new Set([...a, ...b])]

let c = co.filter(item => !a.includes(item) || !b.includes(item))

console.log(c)