Re-think the Quote Backlink implementation.

Before this rewrite, containers and backlinks were created even if the relevant
post did not exist in the page. If the post would never end up existing, it
resulted in a waste of resources. QuoteBacklink's cache also prevented these
containers and backlinks from being garbage collected.
We now only store a map of fullIDs. This feature should be faster since less
elements gets allocated, although the difference is probably negligible.

src/Quotelinks/QuoteBacklink.coffee

@@ -3,19 +3,19 @@ QuoteBacklink =
   #  - previous, same, and following posts.
   #  - existing and yet-to-exist posts.
   #  - newly fetched posts.
-  #  - in copies.
+  #  - clones.
   # XXX what about order for fetched posts?
   #
-  # First callback creates backlinks and add them to relevant containers.
-  # Second callback adds relevant containers into posts.
-  # This is is so that fetched posts can get their backlinks,
-  # and that as much backlinks are appended in the background as possible.
+  # First callback creates a map of quoted -> [quoters],
+  # and append backlinks to posts that already have containers.
+  # Second callback creates, fill and append containers.
   init: ->
     return if !Conf['Quote Backlinks']
 
     format = Conf['backlink'].replace /%id/g, "' + id + '"
     @funk  = Function 'id', "return '#{format}'"
-    @containers = {}
+    @frag  = $.nodes [$.tn(' '), $.el 'a', className: 'backlink']
+    @map   = {}
     Post.callbacks.push
       name: 'Quote Backlinking Part 1'
       cb:   @firstNode
@@ -23,42 +23,39 @@ QuoteBacklink =
       name: 'Quote Backlinking Part 2'
       cb:   @secondNode
   firstNode: ->
-    return if @isClone or !@quotes.length
-    text = QuoteBacklink.funk @ID
-    a = $.el 'a',
-      href: "/#{@board}/res/#{@thread}#p#{@}"
-      className: 'backlink'
-      textContent: text
-    if @isHidden
-      $.addClass a, 'filtered'
-    if @isDead
-      $.addClass a, 'deadlink'
-    if Conf['Quote Markers']
-      QuoteMarkers.parseQuotelink @board, @thread, @, a, false, text
-    for quote in @quotes
-      containers = [QuoteBacklink.getContainer quote]
-      if (post = g.posts[quote]) and post.nodes.backlinkContainer
-        # Don't add OP clones when OP Backlinks is disabled,
-        # as the clones won't have the backlink containers.
-        for clone in post.clones
-          containers.push clone.nodes.backlinkContainer
-      for container in containers
-        link = a.cloneNode true
-        if Conf['Quote Previewing']
-          $.on link, 'mouseover', QuotePreview.mouseover
-        if Conf['Quote Inlining']
-          $.on link, 'click', QuoteInline.toggle
-        $.add container, [$.tn(' '), link]
+    return if @isClone
+    for quoteID in @quotes
+      (QuoteBacklink.map[quoteID] or= []).push @fullID
+      continue unless (post = g.posts[quoteID]) and container = post?.nodes.backlinkContainer
+      for container in [container].concat post.clones.map((clone) -> clone.nodes.backlinkContainer)
+        $.add container, QuoteBacklink.buildBacklink @
     return
   secondNode: ->
-    if @isClone and (@origin.isReply or Conf['OP Backlinks'])
-      @nodes.backlinkContainer = $ '.container', @nodes.info
-      return
     # Don't backlink the OP.
     return unless @isReply or Conf['OP Backlinks']
-    container = QuoteBacklink.getContainer @fullID
-    @nodes.backlinkContainer = container
+    if @isClone
+      @nodes.backlinkContainer = $ '.backlink-container', @nodes.info
+      return
+    @nodes.backlinkContainer = container = $.el 'span',
+      className: 'backlink-container'
+    if @fullID of QuoteBacklink.map
+      for quoteID in QuoteBacklink.map[@fullID]
+        if post = g.posts[quoteID] # Post hasn't been collected since.
+          $.add container, QuoteBacklink.buildBacklink post
     $.add @nodes.info, container
-  getContainer: (id) ->
-    @containers[id] or=
-      $.el 'span', className: 'container'
+  buildBacklink: (post) ->
+    frag = QuoteBacklink.frag.cloneNode true
+    a = frag.lastElementChild
+    a.href = "/#{post.board}/res/#{post.thread}#p#{post}"
+    a.textContent = text = QuoteBacklink.funk post.ID
+    if post.isDead
+      $.addClass a, 'deadlink'
+    if post.isHidden
+      $.addClass a, 'filtered'
+    if Conf['Quote Markers']
+      QuoteMarkers.parseQuotelink post.board, post.thread, post, a, false, text
+    if Conf['Quote Previewing']
+      $.on a, 'mouseover', QuotePreview.mouseover
+    if Conf['Quote Inlining']
+      $.on a, 'click', QuoteInline.toggle
+    frag