var chapter_list = new Array(
  ["Ch.001.1","c001.1"],
  ["Ch.001.2","c001.2"],
  ["Ch.002.1","c002.1"],
  ["Ch.002.2","c002.2"],
  ["Ch.003.1","c003.1"],
  ["Ch.003.2","c003.2"],
  ["Ch.003.3","c003.3"],
  ["Ch.003.4","c003.4"],
  ["Ch.004.1","c004.1"],
  ["Ch.004.2","c004.2"],
  ["Ch.005.1","c005.1"],
  ["Ch.005.2","c005.2"],
  ["Ch.006.1","c006.1"],
  ["Ch.006.2","c006.2"],
  ["Ch.007.1","c007.1"],
  ["Ch.007.2","c007.2"],
  ["Ch.008.1","c008.1"],
  ["Ch.008.2","c008.2"],
  ["Ch.009.1","c009.1"],
  ["Ch.009.2","c009.2"],
  ["Ch.010","c010"],
  ["Ch.011","c011"],
  ["Vol.04 Ch.012","v04/c012"],
  ["Vol.04 Ch.013","v04/c013"],
  ["Vol.04 Ch.014","v04/c014"],
  ["Vol.04 Ch.015","v04/c015"],
  ["Vol.04 Ch.016","v04/c016"],
  ["Vol.04 Ch.017","v04/c017"]
);

var total_chapters = 28;

for (var i = 0; i < chapter_list.length; i++) {
  document.getElementById('top_chapter_list').options[i] = new Option(chapter_list[i][0], chapter_list[i][1]);
  document.getElementById('bottom_chapter_list').options[i] = new Option(chapter_list[i][0], chapter_list[i][1]);
}
document.getElementById('top_chapter_list').value=current_chapter;
document.getElementById('bottom_chapter_list').value=current_chapter;
var current_chapter_index = document.getElementById('top_chapter_list').selectedIndex;