From 9cb60ab960b7bba484a310342c5ffeb7d047a893 Mon Sep 17 00:00:00 2001
From: Carlos Edu Js <carloseduardogit@gmail.com>
Date: Thu, 15 Jan 2026 12:32:41 -0300
Subject: [PATCH 1/2] [DevTools] Fix high CPU usage on pages without React
 (#35515)

Stop polling for React after 10 attempts (~5 seconds) to prevent
infinite loop of 'hello' messages on pages without React.

Fixes #35515
---
 .../react-devtools-extensions/src/contentScripts/proxy.js | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/packages/react-devtools-extensions/src/contentScripts/proxy.js b/packages/react-devtools-extensions/src/contentScripts/proxy.js
index a4e7dd68241..5d4a8eb67e5 100644
--- a/packages/react-devtools-extensions/src/contentScripts/proxy.js
+++ b/packages/react-devtools-extensions/src/contentScripts/proxy.js
@@ -22,11 +22,19 @@ function injectProxy({target}: {target: any}) {
     // The backend waits to install the global hook until notified by the content script.
     // In the event of a page reload, the content script might be loaded before the backend manager is injected.
     // Because of this we need to poll the backend manager until it has been initialized.
+    // We limit retries to avoid high CPU usage on pages without React (see issue #35515).
+    let retryCount = 0;
+    const maxRetries = 10; // Stop polling after ~5 seconds (10 * 500ms)
+
     const intervalID: IntervalID = setInterval(() => {
       if (backendInitialized) {
         clearInterval(intervalID);
+      } else if (retryCount >= maxRetries) {
+        // Stop polling on pages without React to prevent high CPU usage
+        clearInterval(intervalID);
       } else {
         sayHelloToBackendManager();
+        retryCount++;
       }
     }, 500);
   }

From 11f5691d48f95eb346fade4f1f014bf8a6a2efa3 Mon Sep 17 00:00:00 2001
From: Carlos Edu Js <carloseduardogit@gmail.com>
Date: Thu, 15 Jan 2026 23:34:27 -0300
Subject: [PATCH 2/2] [DevTools] Refactor handshake to be event-driven (#35515)

Replaces the polling mechanism in proxy.js with an event-driven approach.
backendManager.js now dispatches a 'react-devtools-ready' event and sets
a data attribute when initialized. This eliminates CPU usage on non-React
pages by removing the need for a polling loop.
---
 .../src/contentScripts/backendManager.js      |  8 +++++
 .../src/contentScripts/proxy.js               | 31 +++++++++----------
 2 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/packages/react-devtools-extensions/src/contentScripts/backendManager.js b/packages/react-devtools-extensions/src/contentScripts/backendManager.js
index 402a1378576..8969bf7bedf 100644
--- a/packages/react-devtools-extensions/src/contentScripts/backendManager.js
+++ b/packages/react-devtools-extensions/src/contentScripts/backendManager.js
@@ -207,4 +207,12 @@ if (!window.__REACT_DEVTOOLS_BACKEND_MANAGER_INJECTED__) {
   window.__REACT_DEVTOOLS_BACKEND_MANAGER_INJECTED__ = true;
 
   window.addEventListener('message', welcome);
+
+  // Signal to the content script that the backend manager has been injected.
+  // This allows the content script to connect immediately without polling.
+  window.document.documentElement.setAttribute(
+    'data-react-devtools-ready',
+    'true',
+  );
+  window.dispatchEvent(new CustomEvent('react-devtools-ready'));
 }
diff --git a/packages/react-devtools-extensions/src/contentScripts/proxy.js b/packages/react-devtools-extensions/src/contentScripts/proxy.js
index 5d4a8eb67e5..e7d79a5f959 100644
--- a/packages/react-devtools-extensions/src/contentScripts/proxy.js
+++ b/packages/react-devtools-extensions/src/contentScripts/proxy.js
@@ -17,26 +17,23 @@ function injectProxy({target}: {target: any}) {
     window.__REACT_DEVTOOLS_PROXY_INJECTED__ = true;
 
     connectPort();
-    sayHelloToBackendManager();
 
     // The backend waits to install the global hook until notified by the content script.
     // In the event of a page reload, the content script might be loaded before the backend manager is injected.
-    // Because of this we need to poll the backend manager until it has been initialized.
-    // We limit retries to avoid high CPU usage on pages without React (see issue #35515).
-    let retryCount = 0;
-    const maxRetries = 10; // Stop polling after ~5 seconds (10 * 500ms)
-
-    const intervalID: IntervalID = setInterval(() => {
-      if (backendInitialized) {
-        clearInterval(intervalID);
-      } else if (retryCount >= maxRetries) {
-        // Stop polling on pages without React to prevent high CPU usage
-        clearInterval(intervalID);
-      } else {
-        sayHelloToBackendManager();
-        retryCount++;
-      }
-    }, 500);
+    // Because of this we need to synchronize with the backend manager.
+    // We use a data attribute and a custom event to detect when the backend manager is ready,
+    // avoiding the need for CPU-intensive polling (see issue #35515).
+
+    const onBackendReady = () => {
+      window.removeEventListener('react-devtools-ready', onBackendReady);
+      sayHelloToBackendManager();
+    };
+
+    if (document.documentElement.getAttribute('data-react-devtools-ready')) {
+      onBackendReady();
+    } else {
+      window.addEventListener('react-devtools-ready', onBackendReady);
+    }
   }
 }