var chap_array = new Array(
    ["8 - Chapter 8 END",'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]);
    }
}