symetric-5.js

function sym(...args) {
    return args.reduce( (a,b,i) => {
        return [...new Set([
            ...a.filter(item => !b.find(aux=>aux===item)),
            ...b.filter(item => !a.find(aux=>aux===item) )
        ].sort((a,b)=>a-b))]
    },[]);
}