wip: add strict mode question

src/data/question-groups/react/content/strict-mode.md

@@ -0,0 +1,19 @@
+Strict Mode is a tool in React for highlighting potential problems in an application. By wrapping a component tree with `StrictMode`, React will activate additional checks and warnings for its descendants. This doesn't affect the production build but provides insights during development.
+
+```js
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <App />
+  </StrictMode>
+);
+```
+
+In Strict Mode, React does a few extra things during development:
+
+1. It renders components twice to catch bugs caused by impure rendering.
+2. It runs side-effects (like data fetching) twice to find mistakes in them caused by missing effect cleanup.
+3. It checks if deprecated APIs are used, and logs a warning message to the console if so.

src/data/question-groups/react/react.md

@@ -295,4 +295,9 @@ questions:
     topics:
       - 'SSR'
       - 'Intermediate'
+  - question: What is Strict Mode in React and why is it useful?
+    answer: strict-mode.md
+    topics:
+      - 'Debugging'
+      - 'Intermediate'
 ---