Help with the rest operator lesson

Tell us what’s happening:

I managed to pass the lesson by adding the rest operator to the provided code, but I then also tried to simplify the code.

I can’t pass the lesson with this code as FCC says that I am not using the rest operator with args…

I get no error in the console, and the code seems to work fine when testing. I am wondering if anyone can tell me what is wrong with this code.


Your code so far

const sum = (...args) => args.reduce((a,b) => a+b, 0)


Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.131 Safari/537.36.

Link to the challenge:

Your code is fine.

This is the regex used to check the submitted code:


As you see it specifically looks for the function keyword.

1 Like

As @jenovs says, technically your code works, but the production tests are a bit picky. The good news is that this challenge’s tests have been rewritten to allow arrow function syntax as you are using here. We are just waiting for the changes to be deployed to production.

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Thanks for the answer!

This was my code answer, and it passed, but it doesn’t seem like it’s actually correct/best practice/using the spread operator:

const sum = (function() {
  "use strict";
return function sum(...args) {
    const num = [ 1, 2, 3];
    return args.reduce((a, b) => a + b, 0);

console.log(sum(1, 2, 3)); // 6

num isn’t used for anything so delete that line, looks absolutely fine otherwise.

thanks! i spent probably 20 minutes trying different things on this one.