Find the Symmetric Difference Please help

Tell us what’s happening:

Your code so far

function sym(args) {
  return args;

sym([1, 2, 3], [5, 2, 1, 4]);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.80 Safari/537.36.

Link to the challenge:

I can’t understand this challenge anybody can help me!

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