var chap_array = new Array(
    ["13 - Chapter 13",'13'],

    ["12 - Chapter 12",'12'],

    ["11 - Chapter 11",'11'],

    ["Side Story - Shoot!!",'10.1'],

    ["10 - Chapter 10",'10'],

    ["9 - Chapter 9",'9'],

    ["8 - Chapter 8",'8'],

    ["7 - Chapter 7",'7'],

    ["6 - Chapter 6",'6'],

    ["5 - Chapter 5",'5'],

    ["4 - Chapter 4",'4'],

    ["3 - Chapter 3",'3'],

    ["2 - Chapter 2",'2'],

    ["1 - Chapter 1",'1']
);
for (var i=0; i<chap_array.length; i++) {
    document.getElementById('id_chapter_1').options[i] = new Option(chap_array[i][0],chap_array[i][1]);
    if (document.getElementById('id_chapter_2')) {
        document.getElementById('id_chapter_2').options[i] = new Option(chap_array[i][0],chap_array[i][1]);
    }
}