DNA Pairing - Arrow function not working

I currently have this answer that works fine

function pairElement(str) {
  let dnaStr = [];
  dnaStr = str.split('').map( function(x) {
    switch(x) {
      case 'A': return ['A','T'];
      break;

      case 'T': return ['T','A'];
      break;

      case 'C': return ['C','G'];
      break;

      case 'G': return ['G','C'];
      break;

    };
  });
  return dnaStr;
}

pairElement("ATCGA");

Why does this not work if i change the function within the map argument to an arrow function format like this:

function pairElement(str) {
  let dnaStr = [];
  dnaStr = str.split('').map( x =>  (
    switch(x) {
      case 'A': return ['A','T'];
      break;

      case 'T': return ['T','A'];
      break;

      case 'C': return ['C','G'];
      break;

      case 'G': return ['G','C'];
      break;

    };
  ));
  return dnaStr;
}

pairElement("ATCGA");

I get a syntax error. Why does the arrow function format not work. Have i written that incorrectly?

Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:66.0) Gecko/20100101 Firefox/66.0.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/dna-pairing

You need to replace the ( on the far right in the following line with a {

dnaStr = str.split('').map( x =>  (

and replace the first ) in the following line right before the return statement with a }.

  ));

FYI - You can go ahead and just initialize dnaStr like:

let dnaStr = str.split('').map( ...................