var chapter_list = new Array(
  ["Vol.01 Ch.001: Passionate Electric Waves  Vol 1 Ch. 1.0","v01/c001"],
  ["Vol.01 Ch.002: Passionate Electric Waves  Vol 1 Ch. 2.0","v01/c002"]
);

var total_chapters = 2;

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;