text: function unite(arr1, arr2, arr3) {
    var argsArray = [].slice.apply(arguments)
    var final = [];
  
    final = argsArray.reduce(function(prev, cur) {
      return prev.concat(cur.filter(function (elem) {
        return (prev.indexOf(elem) == -1);
      }));
    });
  
    return final;
  }
  
  console.log(unite([1, 3, 2], [5, 2, 1, 4], [2, 1]));
  