$.xhr will now deal with Last-Modified and If-Modified-Since headers itself.

lib/$.coffee

@@ -36,17 +36,23 @@ $.extend = (object, properties) ->
   for key, val of properties
     object[key] = val
   return
-$.ajax = (url, options, extra={}) ->
-  {type, headers, upCallbacks, form, sync} = extra
-  r = new XMLHttpRequest()
-  type or= form and 'post' or 'get'
-  r.open type, url, !sync
-  for key, val of headers
-    r.setRequestHeader key, val
-  $.extend r, options
-  $.extend r.upload, upCallbacks
-  r.send form
-  r
+$.ajax = do ->
+  # Status Code 304: Not modified
+  # With the `If-Modified-Since` header we only receive the HTTP headers and no body for 304 responses.
+  # This saves a lot of bandwidth and CPU time for both the users and the servers.
+  lastModified = {}
+  (url, options, extra={}) ->
+    {type, whenModified, upCallbacks, form, sync} = extra
+    r = new XMLHttpRequest()
+    type or= form and 'post' or 'get'
+    r.open type, url, !sync
+    if whenModified
+      r.setRequestHeader 'If-Modified-Since', lastModified[url] or '0'
+      $.on r, 'load', -> lastModified[url] = r.getResponseHeader 'Last-Modified'
+    $.extend r, options
+    $.extend r.upload, upCallbacks
+    r.send form
+    r
 $.cache = do ->
   reqs = {}
   (url, cb, options) ->

src/Monitoring/ThreadStats.coffee

@@ -8,7 +8,6 @@ ThreadStats =
     @postCountEl  = $ '#post-count', @dialog
     @fileCountEl  = $ '#file-count', @dialog
     @pageCountEl  = $ '#page-count', @dialog
-    @lastModified = '0'
 
     Thread::callbacks.push
       name: 'Thread Stats'
@@ -41,9 +40,8 @@ ThreadStats =
       return
     setTimeout ThreadStats.fetchPage, 2 * $.MINUTE
     $.ajax "//api.4chan.org/#{ThreadStats.thread.board}/threads.json", onload: ThreadStats.onThreadsLoad,
-      headers: 'If-Modified-Since': ThreadStats.lastModified
+      whenModified: true
   onThreadsLoad: ->
-    ThreadStats.lastModified = @getResponseHeader 'Last-Modified'
     return if @status isnt 200
     pages = JSON.parse @response
     for page in pages

src/Monitoring/ThreadUpdater.coffee

@@ -25,7 +25,6 @@ ThreadUpdater =
     ThreadUpdater.root         = @OP.nodes.root.parentNode
     ThreadUpdater.lastPost     = +ThreadUpdater.root.lastElementChild.id.match(/\d+/)[0]
     ThreadUpdater.outdateCount = 0
-    ThreadUpdater.lastModified = '0'
 
     for input in $$ 'input', ThreadUpdater.dialog
       if input.type is 'checkbox'
@@ -95,7 +94,6 @@ ThreadUpdater =
         when 200
           g.DEAD = false
           ThreadUpdater.parse JSON.parse(req.response).posts
-          ThreadUpdater.lastModified = req.getResponseHeader 'Last-Modified'
           ThreadUpdater.set 'timer', ThreadUpdater.getInterval()
         when 404
           g.DEAD = true
@@ -108,12 +106,7 @@ ThreadUpdater =
             thread: ThreadUpdater.thread
         else
           ThreadUpdater.outdateCount++
-          ThreadUpdater.set 'timer',  ThreadUpdater.getInterval()
-          ###
-          Status Code 304: Not modified
-          By sending the `If-Modified-Since` header we get a proper status code, and no response.
-          This saves bandwidth for both the user and the servers and avoid unnecessary computation.
-          ###
+          ThreadUpdater.set 'timer', ThreadUpdater.getInterval()
           [text, klass] = if req.status is 304
             [null, null]
           else
@@ -159,7 +152,7 @@ ThreadUpdater =
       ThreadUpdater.req.abort()
     url = "//api.4chan.org/#{ThreadUpdater.thread.board}/res/#{ThreadUpdater.thread}.json"
     ThreadUpdater.req = $.ajax url, onloadend: ThreadUpdater.cb.load,
-      headers: 'If-Modified-Since': ThreadUpdater.lastModified
+      whenModified: true
 
   updateThreadStatus: (title, OP) ->
     titleLC = title.toLowerCase()