WebUI: Don't update UI if the page is hidden

Currently, there is unnecessary CPU/network usage by the web UI when it's running in the background, this PR prevents it from refreshing in the background.

Closes #22565.
PR #22567.

src/webui/www/private/scripts/client.js

@@ -750,6 +750,8 @@ window.addEventListener("DOMContentLoaded", () => {
     let syncMainDataTimeoutID = -1;
     let syncRequestInProgress = false;
     const syncMainData = () => {
+        if (document.hidden)
+            return;
         syncRequestInProgress = true;
         const url = new URL("api/v2/sync/maindata", window.location);
         url.search = new URLSearchParams({
@@ -1774,6 +1776,21 @@ window.addEventListener("DOMContentLoaded", () => {
             }
         }
     });
+
+    addEventListener("visibilitychange", (event) => {
+        if (document.hidden)
+            return;
+
+        switch (LocalPreferences.get("selected_window_tab")) {
+            case "log":
+                window.qBittorrent.Log.load();
+                break;
+            case "transfers":
+                syncData(100);
+                updatePropertiesPanel();
+                break;
+        }
+    });
 });
 
 window.addEventListener("load", async () => {