Add Items to an Array with push() and unshift() using variables

Tell us what’s happening:

I don’t know why this code won’t pass. In the output file it shows that it is working but when I run the tests it does not work. Would like to understand why.

Your code so far


function mixedNumbers(arr) {
  // change code below this line
    let arrStart = ['I', 2, 'three'];
    let arrEnd = [7, 'VIII', 9];
    arr.unshift(arrStart);
    arr.push(arrEnd);
  // change code above this line
  return arr;
}

// do not change code below this line
console.log(mixedNumbers(['IV', 5, 'six']));

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/basic-data-structures/add-items-to-an-array-with-push-and-unshift

[["I", 2, "three"], "IV", 5, "six", [7, "VIII", 9]]

The correct syntax is arr.unshift('I', 2, 'three') or arr.unshift(...arrStart)
The push call is the same