Issue with Problem 20 using Javascript and function in for loop

Hi all, I'm having a difficult time with problem 20 using the code below. For whatever reason, when I run it using JavaScript, only the first value is added to the answer line. I'm not sure what I'm doing wrong. I solved the farenheit to celsius problem in a very similar way, and did not experience this issue. My function seems to be working correctly, because when I try something like countVowels('aaahhheeennn'), it returns 6. Could someone help me out?

var counter = input();
var vowels = ['a', 'e', 'i', 'o', 'u', 'y'];
var s = new String;

function countVowels(str) {
    str = str.toLowerCase();
    var count = new Number;

    for (i = 0; i < str.length; i++) {
        if (vowels.indexOf(str[i]) !== -1) {
            count = count + 1;
        }
    }
    return count;
}

for (i = 0; i < counter; i++) {
    s = s + countVowels(input()) + ' ';
}

output(s);