client/polyfill: add .querySelector to NodeList

client/js/util/polyfill.js

@@ -3,6 +3,19 @@
 // fix iterating over NodeList in Chrome and Opera
 NodeList.prototype[Symbol.iterator] = Array.prototype[Symbol.iterator];
 
+NodeList.prototype.querySelector = function(...args) {
+    for (let node of this) {
+        if (node.nodeType === 3) {
+            continue;
+        }
+        const result = node.querySelector(...args);
+        if (result) {
+            return result;
+        }
+    }
+    return null;
+}
+
 // non standard
 Node.prototype.prependChild = function(child) {
     if (this.firstChild) {