Symmetric Difference: tests failing

Tell us what’s happening:
I’ve solved this challenge and input it into the fcc interface. The results displayed (console.log) match those outlined on the challenge page, but every single test reports failure when I check them.
I’ve been working in PythonTutor to see it run live and I get the desired results there as well.
Any idea why this isn’t passing?

Your code so far

  // convert object to array
  args =;

// check that item in position doesn't = item in position immediately before it, returns only unique values
 function single(a) {
  return a.sort().filter(function(el, pos, ary) {
   return !pos || el != ary[pos-1];
 function duplicates(b) {
  b.forEach(function(el) {
   return b.filter(function(el, pos, ary) {
      var firstPos = b.indexOf(el);
      // remove both item & value in position that matched
      if (firstPos !== pos) {
        b.splice(firstPos, 1);
        b.splice(pos-1, 1); 
 var arr1 = arguments[0];
  for (var a = 1; a < args.length; a++) {
    arr1 = single(arr1);
    var arr2 = arguments[a];
    arr2 = single(arr2);
    var merged = arr1.concat(arr2);
    arr1 = merged;

 var sorted = arr1.sort();
  return sorted;

sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3], [5, 3, 9, 8], [1]);

Your browser information:

Your Browser User Agent is: Chrome Version 63.0.3239.84 (Official Build) (64-bit).

Link to the challenge:

You can see the console.log's output on the browser console. I have no idea why the output on the challenge page outputs the expected value, but the values on the console are quite different.

Removing the args from the parameter list solves the challenge? Interesting…

I think I’ve figured it out. You have stored arguments as a proper array in the args variable, but you still directly referenced arguments later in the code twice. Since args now holds all of the arguments in one array, arguments[0] actually refers to all of them (arguments[0] == args since args is the first parameter in the parameter list), not just the first arg. Changing arguments to args should fix the bug.

This worked. Thank you!