var chapter_list = new Array(
  ["Vol.01 Ch.001.1","v01/c001.1"],
  ["Vol.01 Ch.001.2","v01/c001.2"],
  ["Vol.01 Ch.002.1","v01/c002.1"],
  ["Vol.01 Ch.002.2","v01/c002.2"],
  ["Vol.01 Ch.003.1","v01/c003.1"],
  ["Vol.01 Ch.003.2","v01/c003.2"],
  ["Vol.02 Ch.004.1","v02/c004.1"],
  ["Vol.02 Ch.004.2","v02/c004.2"],
  ["Vol.02 Ch.005.1","v02/c005.1"],
  ["Vol.02 Ch.005.2","v02/c005.2"],
  ["Vol.02 Ch.006.1","v02/c006.1"],
  ["Vol.02 Ch.006.2","v02/c006.2"],
  ["Vol.03 Ch.007.1","v03/c007.1"],
  ["Vol.03 Ch.007.2","v03/c007.2"],
  ["Vol.03 Ch.008","v03/c008"],
  ["Vol.04 Ch.001: Full volume","v04/c001"],
  ["Vol.05 Ch.011.1","v05/c011.1"],
  ["Vol.05 Ch.011.2","v05/c011.2"],
  ["Vol.05 Ch.011.3","v05/c011.3"],
  ["Vol.05 Ch.012","v05/c012"],
  ["Vol.05 Ch.013","v05/c013"],
  ["Vol.06 Ch.014","v06/c014"],
  ["Vol.06 Ch.015","v06/c015"]
);

var total_chapters = 23;

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;