var chap_array = new Array(
    ["12 - Futari no Sekai",'12'],

    ["11 - Twisted Thoughts",'11'],

    ["10 - Couple and Single",'10'],

    ["9 - Mask",'9'],

    ["8 - The Thoughts of the Two",'8'],

    ["7 - Warmth",'7'],

    ["6 - Right Hand and Left Hand",'6'],

    ["5 - The Story Begins",'5'],

    ["4 - Another Charm",'4'],

    ["3 - First Kiss",'3'],

    ["2 - The Couple's Distance",'2'],

    ["1 - Confession",'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]);
    }
}