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","v01/c002"],
  ["Vol.01 Ch.003.1","v01/c003.1"],
  ["Vol.01 Ch.003.2","v01/c003.2"],
  ["Vol.01 Ch.004","v01/c004"],
  ["Vol.01 Ch.005","v01/c005"],
  ["Vol.02 Ch.006","v02/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.03 Ch.011","v03/c011"],
  ["Vol.03 Ch.012: love wan chapter 12","v03/c012"]
);

var total_chapters = 14;

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;