var chapter_list = new Array(
  ["Vol.01 Ch.001","v01/c001"],
  ["Vol.01 Ch.002","v01/c002"],
  ["Vol.01 Ch.003","v01/c003"],
  ["Vol.01 Ch.004","v01/c004"],
  ["Vol.01 Ch.005","v01/c005"],
  ["Vol.01 Ch.006","v01/c006"],
  ["Vol.02 Ch.007","v02/c007"],
  ["Vol.02 Ch.008","v02/c008"],
  ["Vol.02 Ch.009","v02/c009"],
  ["Vol.02 Ch.010","v02/c010"],
  ["Vol.02 Ch.011","v02/c011"],
  ["Vol.02 Ch.012","v02/c012"],
  ["Vol.02 Ch.013","v02/c013"],
  ["Vol.02 Ch.014","v02/c014"],
  ["Vol.03 Ch.015: Chapter 15-16","v03/c015"],
  ["Vol.03 Ch.017: CH.17-19","v03/c017"],
  ["Vol.03 Ch.020","v03/c020"],
  ["Vol.04 Ch.021: Chapter 21 and 22","v04/c021"],
  ["Vol.04 Ch.023: Chapter 23 to 27","v04/c023"],
  ["Vol.05 Ch.028","v05/c028"],
  ["Vol.05 Ch.029","v05/c029"],
  ["Vol.05 Ch.030","v05/c030"],
  ["Vol.05 Ch.031","v05/c031"],
  ["Vol.05 Ch.032","v05/c032"],
  ["Vol.05 Ch.033","v05/c033"],
  ["Vol.05 Ch.034","v05/c034"],
  ["Vol.05 Ch.035","v05/c035"],
  ["Vol.05 Ch.036","v05/c036"]
);

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;