var chap_array = new Array(
    ["Side Story - Yuuki Natsuno - A Day in the Life of Murasako Masao",'4.5'],

    ["4 - Yuuki Natsuno 4",'4'],

    ["3 - Yuuki Natsuno 3",'3'],

    ["2 - Yuuki Natsuno 2",'2'],

    ["1 - Yuuki Natsuno",'1'],

    ["0 - Prologue",'0']
);
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]);
    }
}