JavaScript - Mutations

I run my code in Node.js (v10.17.0) on my local machine (Ubuntu 18.04.3 LTS) and it pass all of the test, but does not pass in freeCodeCamp. Any ideas?

Here is my code:

function mutations(arr) {
    // change both strings to lowercase
    str1 = arr[0].toLowerCase();
    str2 = arr[1].toLowerCase();
    // loop through each letter in 2nd string
    for (var i = 0; i < str2.length; i++) {
        //console.log(str2[i]); // TEST: verify each letter
        //check if letter is in 1st string
        if (str1.indexOf(str2[i]) === -1) {
            return false;
    return true;

console.log(mutations(["hello", "hey"]));
console.log(mutations(["Alien", "line"]));
console.log(mutations(["Hello", "hello"]));
console.log(mutations(["Mary", "army"]));
console.log(mutations(["ate", "date"]));
console.log(mutations(["zyxwvutsrqponmlkjihgfedcba", "qrstu"]));

Make sure to declare all variables and make sure to not change the name of the function.

Thank you Randell. I am sorry for such a trivial mistake. That resolve it! I’m just glad I did not spend too much time on it and asked for help. Have a good evening.