var chapter_list = new Array(
  ["Vol.001 Ch.001","v001/c001"],
  ["Vol.01 Ch.002: Service","v01/c002"],
  ["Vol.01 Ch.003: Service 3","v01/c003"],
  ["Vol.01 Ch.004: Service 4","v01/c004"],
  ["Vol.01 Ch.005: Service 5","v01/c005"],
  ["Vol.01 Ch.005.1: Omake","v01/c005.1"],
  ["Vol.02 Ch.006: Service 6","v02/c006"],
  ["Vol.02 Ch.007: Service 7","v02/c007"],
  ["Vol.02 Ch.008: Service 8","v02/c008"]
);

var total_chapters = 9;

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;