Use the Rest Operator with Function Parameters --- Need Help , Thanks

Tell us what’s happening:
my code does not pass the last test , i don’t know WHY?

Your code so far

const sum = (function() {
  "use strict";
  return function sum(...x) {
    return x.reduce((y,z) => y+z,0);
console.log(sum()); // 6

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.110 Safari/537.36.

Link to the challenge:

Try replacing x with args. Some of the tests check that you’ve modified the existing code, so if you change variable names those tests tend to break.