var chapter_list = new Array(
  ["Ch.001.1","c001.1"],
  ["Ch.001.2","c001.2"],
  ["Ch.002.1","c002.1"],
  ["Ch.002.2","c002.2"],
  ["Ch.003.1","c003.1"],
  ["Ch.003.2","c003.2"],
  ["Ch.004.1","c004.1"],
  ["Ch.004.2","c004.2"],
  ["Ch.005.1","c005.1"],
  ["Ch.005.2","c005.2"],
  ["Ch.006.1","c006.1"],
  ["Ch.006.2","c006.2"],
  ["Ch.007","c007"],
  ["Ch.008","c008"],
  ["Ch.009","c009"],
  ["Ch.010","c010"],
  ["Ch.011","c011"],
  ["Ch.012","c012"],
  ["Ch.013","c013"],
  ["Ch.014","c014"],
  ["Ch.015","c015"],
  ["Ch.016","c016"],
  ["Ch.017","c017"],
  ["Ch.018","c018"],
  ["Ch.019","c019"],
  ["Ch.020","c020"],
  ["Ch.021","c021"],
  ["Ch.022","c022"],
  ["Ch.023","c023"],
  ["Ch.024","c024"],
  ["Ch.025","c025"],
  ["Ch.026","c026"],
  ["Ch.027","c027"],
  ["Ch.028","c028"],
  ["Ch.029","c029"],
  ["Ch.030","c030"],
  ["Ch.031","c031"],
  ["Ch.032","c032"],
  ["Ch.033","c033"],
  ["Ch.034","c034"],
  ["Ch.035","c035"],
  ["Ch.036","c036"],
  ["Ch.037","c037"],
  ["Ch.038","c038"],
  ["Ch.039","c039"],
  ["Ch.040","c040"],
  ["Ch.041","c041"],
  ["Ch.042","c042"]
);

var total_chapters = 48;

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;