web/src/app.jsx

@@ -858,14 +858,23 @@ function App() {
         method: "POST",
         body: JSON.stringify({ command: "JOIN", to: name }),
       });
+      // Show the channel's tab. Preact runs this update at once on the
+      // newest tab list, so the tab is found there by name: the user's
+      // own JOIN event may already have added it, and other tabs may
+      // have closed.
       setTabs((prev) => {
-        if (prev.find((t) => t.type === "channel" && t.name === name))
+        const idx = prev.findIndex(
+          (t) => t.type === "channel" && t.name === name,
+        );
+        if (idx >= 0) {
+          setActiveTab(idx);
+
           return prev;
+        }
+        setActiveTab(prev.length);
 
         return [...prev, { type: "channel", name }];
       });
-      const newIdx = tabsRef.current.length;
-      setActiveTab(newIdx);
       try {
         const hist = await api(
           `/history?target=${encodeURIComponent(name)}&limit=50`,