FCC BAS #14 - Bonfire: Mutations

function mutation(arr) {
    var one = arr[0].toLowerCase();
    var two = arr[1].toLowerCase().split('');
    for(x=0; x<two.length; x++) {
        if(one.indexOf(two[x]) === -1) {
            return false;
        }
    } return true;
}
mutation(['hello', 'hey']);