Trying to solve symmetric difference using Javascript

Question

I am trying to figure out a solution for symmetric difference using javascript that accomplishes the following objectives:

• accepts an unspecified number of ar

Answer 1

Alternative: Use the lookup inside a map instead of an array

function sym(...vs){
    var has = {};
    //flatten values
    vs.reduce((a,b)=>a.concat(b)).
        //if element does not exist add it (value==1)
        //or mark it as multiply found value > 1
        forEach(value=>{has[value] = (has[value]||0)+1});
    return Object.keys(has).filter(x=>has[x]==1).map(x=>parseInt(x,10));
}
console.log(sym([1, 2, 3], [5, 2, 1, 4],[5,7], [5]));//[3,4,7])