var chap_array = new Array(
["Spiral 5",'spiral-5'],
["Spiral 4",'spiral-4'],
["Spiral 2",'spiral-2'],
["Spiral 1",'spiral-1']);

for (var i=0; i<chap_array.length; i++) {
document.getElementById('chapter_select').options[i] = new Option(chap_array[i][0],chap_array[i][1]);
}