var chapter_list = new Array(
  ["Vol.01 Ch.001: Prologue / Altar of Blood","v01/c001"],
  ["Vol.02 Ch.002: Mary","v02/c002"],
  ["Vol.03 Ch.003: Prologue / Possessions","v03/c003"],
  ["Vol.04 Ch.004: Invitation to my dream / Memory / Scissors","v04/c004"],
  ["Vol.05 Ch.005: Freesia","v05/c005"],
  ["Vol.06 Ch.006: Vampire","v06/c006"],
  ["Vol.07 Ch.007: Choice","v07/c007"]
);

var total_chapters = 7;

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;