Add Index/Reply Navigation.

This code is so old.
Are these features even used?

css/style.css

@@ -54,7 +54,7 @@ a[href="javascript:;"] {
 /* fixed, z-index */
 #qp, #ihover,
 #updater, #thread-stats,
-#header,
+#navlinks, #header,
 #qr, #watcher {
   position: fixed;
 }
@@ -67,7 +67,7 @@ a[href="javascript:;"] {
 #menu {
   z-index: 60;
 }
-#updater, #thread-stats {
+#navlinks, #updater, #thread-stats {
   z-index: 50;
 }
 #header:hover {
@@ -304,6 +304,13 @@ a[href="javascript:;"] {
   padding-bottom: 16px;
 }
 
+/* Index/Reply Navigation */
+#navlinks {
+  font-size: 16px;
+  top: 25px;
+  right: 10px;
+}
+
 /* Filter */
 .opContainer.filter-highlight {
   box-shadow: inset 5px 0 rgba(255, 0, 0, .5);

src/features.coffee

@@ -1025,6 +1025,58 @@ ArchiveLink =
       open: open
     }
 
+Nav =
+  init: ->
+    span = $.el 'span',
+      id: 'navlinks'
+    prev = $.el 'a',
+      textContent: '▲'
+      href: 'javascript:;'
+    next = $.el 'a',
+      textContent: '▼'
+      href: 'javascript:;'
+
+    $.on prev, 'click', @prev
+    $.on next, 'click', @next
+
+    $.add span, [prev, $.tn(' '), next]
+    $.on d, '4chanXInitFinished', -> $.add d.body, span
+
+  prev: ->
+    if g.VIEW is 'reply'
+      window.scrollTo 0, 0
+    else
+      Nav.scroll -1
+
+  next: ->
+    if g.VIEW is 'reply'
+      window.scrollTo 0, d.body.scrollHeight
+    else
+      Nav.scroll +1
+
+  getThread: (full) ->
+    headRect  = $.id('header-bar').getBoundingClientRect()
+    topMargin = headRect.top + headRect.height
+    threads = $$ '.thread:not([hidden])'
+    for thread, i in threads
+      rect = thread.getBoundingClientRect()
+      if rect.bottom > topMargin # not scrolled past
+        return if full then [threads, thread, i, rect, topMargin] else thread
+    return $ '.board'
+
+  scroll: (delta) ->
+    [threads, thread, i, rect, topMargin] = Nav.getThread true
+    top = rect.top - topMargin
+
+    # unless we're not at the beginning of the current thread
+    # (and thus wanting to move to beginning)
+    # or we're above the first thread and don't want to skip it
+    unless (delta is -1 and Math.ceil(top) < 0) or (delta is +1 and top > 1)
+      i += delta
+
+    top = threads[i]?.getBoundingClientRect().top - topMargin
+    window.scrollBy 0, top
+
 Redirect =
   image: (board, filename) ->
     # Do not use g.BOARD, the image url can originate from a cross-quote.

src/main.coffee

@@ -344,6 +344,7 @@ Main =
     initFeature 'Thread Stats',             ThreadStats
     initFeature 'Thread Updater',           ThreadUpdater
     initFeature 'Thread Watcher',           ThreadWatcher
+    initFeature 'Index/Reply Navigation',   Nav
     console.timeEnd 'All initializations'
 
     $.on d, '4chanMainInit', Main.initStyle