var chapter_list = new Array(
  ["Vol.01 Ch.001: Story 1","v01/c001"],
  ["Vol.01 Ch.001.1: Story 1","v01/c001.1"],
  ["Vol.01 Ch.001.2: Story 1","v01/c001.2"],
  ["Vol.01 Ch.002.1: Story 1","v01/c002.1"],
  ["Vol.01 Ch.002.2: Story 1","v01/c002.2"],
  ["Vol.01 Ch.003: Story 2","v01/c003"],
  ["Vol.01 Ch.003.2","v01/c003.2"],
  ["Vol.01 Ch.003.3: Story 2","v01/c003.3"],
  ["Vol.01 Ch.004: Story 3","v01/c004"],
  ["Vol.01 Ch.005: Story 4","v01/c005"]
);

var total_chapters = 10;

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;