Add an observer to make sure the hide class is removed when necessary.

data/trello-counter.js

@@ -1,10 +1,29 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-self.port.on("cardCounterRefresh", function() {
+function showCounters() {
   var list = document.getElementsByClassName("list-header-num-cards");
+  if (list === null) setTimeout(showCounters, 100);
   for (var i = 0; i < list.length; i++) {
-    list[i].classList.remove("hide");
+    if (list[i].classList.contains("hide")) {
+      list[i].classList.remove("hide");
+    }
   }
-});
+}
+
+function setupObserver() {
+  console.debug('Init observers');
+  var observer = new MutationObserver(function(mutations) {
+    console.debug("Mutation detected on num cards headers");
+    showCounters();
+  });
+  var list = document.querySelector('.list-header-num-cards');
+  if (list === null) setTimeout(setupObserver, 100);
+  observer.observe(list, {
+    attributes: true,
+    characterData: true
+  });
+}
+
+self.port.on("setupObserver", setupObserver);
+self.port.on("cardCounterRefresh", showCounters);

lib/main.js

@@ -10,6 +10,7 @@ pageMod.PageMod({
   include: "https://trello.com/b/*",
   contentScriptFile: self.data.url("trello-counter.js"),
   onAttach: function(worker) {
+    worker.port.emit("setupObserver");
     worker.port.emit("cardCounterRefresh");
     tabs.on('activate', function () {
       worker.port.emit("cardCounterRefresh");

package.json

@@ -5,5 +5,5 @@
   "description": "Display Trello list number of cards",
   "author": "Rémy HUBSCHER <[email protected]>",
   "license": "MPL 2.0",
-  "version": "0.2"
+  "version": "0.3"
 }