ComikeyDownloader.js

// How to use:
// 1) Go to a chapter page on Comikey.
// 2) Open the console (generally if you open "inspect element"
//    the browser console will be another tab of that).
// 3) Paste this entire file into the console, and hit enter
// 4) Type run() into the console, and hit enter.
// 5) Navigate to another page of the chapter using the left
//    and right arrow keys or the slider bar. You should see
//    an alert telling you which page to go to.
// 6) Repeat (4) and (5) until you see an alert which says
//    "Downloaded all pages".
// 7) Use 7zip or a similar program to combine all of the
//    downloaded page image files into one zip file, then
//    rename the zip file to have the file extension ".cbz"

// Update 2021-12-19: Fixed script to work on chapters that
// use img tags instead of canvas tags (this was previously
// an issue with webtoon-style continuous vertical chapters)

var make_filename = function(page_name){
  return page_name.match(/\d/g).join('').padStart(4, "0");
}

var img_to_canvas = function(img){
  var c = document.createElement("canvas");
  c.width = img.getAttribute("width");
  c.height = img.getAttribute("height");
  var context = c.getContext('2d');
  context.drawImage(img, 0, 0);
  if (!context.getImageData(0, 0, 1, 1).data[3]) {
    return null;
  }
  return c;
}

var download = function(page){
  page_name = page.getAttribute("aria-label");
  var link = document.createElement('a');
  link.download = make_filename(page_name) + ".png";
  if (page.nodeName == "IMG") {
    page = img_to_canvas(page);
    if (!page) {
      return false;
    }
  }
  link.href = page.toDataURL("image/png");
  link.click();
  return true;
}

var grab_first = function(iterable) {
  return iterable.values().next().value;
}

var is_ready_page = function(page) {
  if (page.nodeName == "CANVAS") {
    return (page.getAttribute("width") && page.getAttribute("height"));
  } else if (page.nodeName == "IMG") {
    return (page.getAttribute("src") && page.getAttribute("src").startsWith("blob:"));
  } else {
    return false;
  }
}

if (typeof my_pages === 'undefined' || my_pages === null) {
  var my_pages = new Set(document.querySelectorAll("img.page-img, canvas.page-img"));
  if (my_pages.size === 0) {
    alert("No pages found")
  }
}

var run = function(){
  if (my_pages.size === 0) {
    alert("You have already downloaded all pages");
    return;
  }

  new_pages = new Set(my_pages)
  for (page of my_pages) {
    if  (is_ready_page(page)) {
      var rtn = download(page);
      if (rtn) {
        new_pages.delete(page);
      }
    }
  }
  my_pages = new_pages

  if (my_pages.size === 0) {
    alert("Downloaded all pages")
  } else {
    alert("Remaining pages: " + my_pages.size + " pages, including: " + grab_first(my_pages).getAttribute("aria-label"))
  }
}