var chap_array = new Array(
    ["12 - Volume3 Chapter12",'12'],

    ["11 - Volume3 Chapter11",'11'],

    ["10 - Volume3 Chapter10",'10'],

    ["9 - Volume3 Chapter9",'9'],

    ["8 - Volume2 Chapter8",'8'],

    ["7 - Volume2 Chapter7",'7'],

    ["6 - Volume2 Chapter6",'6'],

    ["5 - Volume2 Chapter5",'5'],

    ["4 - Volume1 Chapter4",'4'],

    ["3 - Volume1 Chapter3",'3'],

    ["2 - Volume1 Chapter2",'2'],

    ["1 - Volume1 Chapter1",'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]);
    }
}