Bonfire: Diff Two Arrays

function diff(arr1, arr2) {    // Same, same; but different.    var newArr = [];    newArr =  arr1.filter(function(x){        if(arr2.indexOf(x) == -1)        {            return x;        }    });    var newArr2 = arr2.filter(function(x){        if(arr1.indexOf(x) ==-1)        {            return x;        }    });    return  newArr.concat(newArr2);}diff([1, 2, 3, 5], [1, 2, 3, 4, 5]);