var chap_array = new Array(
    ["3 - Chapter 3 END",'3/01'],

    ["2 - Chapter 2",'2/01'],

    ["1 - Chapter 1",'1/01']
);
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]);
    }
}