diff --git a/boards/static/js/thread_update.js b/boards/static/js/thread_update.js
--- a/boards/static/js/thread_update.js
+++ b/boards/static/js/thread_update.js
@@ -82,9 +82,6 @@ function connectWebsocket() {
  * missed.
  */
 function getThreadDiff() {
-    var lastPost = threadPosts.last();
-    var threadId = threadPosts.first().attr('id');
-
     var diffUrl = '/api/diff_thread/' + threadId + '/' + lastUpdateTime + '/';
 
     lastUpdateTime = $('.metapanel').attr('data-last-update');