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: Side Story","v01/c004"],
  ["Vol.02 Ch.005: Fallen head over heels","v02/c005"],
  ["Vol.02 Ch.006: Heartthrob Vacation","v02/c006"],
  ["Vol.02 Ch.007: A Small Crush","v02/c007"],
  ["Vol.02 Ch.008: Happy Ending","v02/c008"],
  ["Vol.02 Ch.008.5: Hiroki's Secret","v02/c008.5"]
);

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;