Why isn't splicing working

JavaScript
1

Hello,
please help, I can’t figure out why my splicing is not working

Screenshot_22
Screenshot_22679×624 8.8 KB

3

Thank you for your answer.

function frankenSplice(arr1, arr2, n) {
  let localArr = arr2.slice();
  localArr.splice(n, 0, ...arr1);
  return localArr;
}

Why is this code working? Wasn’t an array also passed here as the third argument?