Due to jQuery propagating events, the window resize event could be triggered by a bubbled event.

See https://bugs.jquery.com/ticket/9841. In our case, the OutputArea was triggering a ‘resize’ event on its element, which was bubbling up and causing this handler to execute every time an output was appended. This was a pretty big drain on output areas that quickly changed (like for interact widgets), presumably since this function involves a DOM read to get heights.

notebook/static/base/js/page.js

@@ -52,9 +52,13 @@ define([
         this._resize_site();
     };
 
-    Page.prototype._resize_site = function() {
+    Page.prototype._resize_site = function(e) {
         // Update the site's size.
-        $('div#site').height($(window).height() - $('#header').height());
+        // only trigger if the event actually is the window's, not bubbling up.
+        // See https://bugs.jquery.com/ticket/9841#comment:8
+        if (!e.target.tagName) {
+            $('div#site').height($(window).height() - $('#header').height());
+        }
     };
 
     return {'Page': Page};