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.agents/skills/vercel-react-best-practices/rules/bundle-preload.md

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+---
+title: Preload Based on User Intent
+impact: MEDIUM
+impactDescription: reduces perceived latency
+tags: bundle, preload, user-intent, hover
+---
+
+## Preload Based on User Intent
+
+Preload heavy bundles before they're needed to reduce perceived latency.
+
+**Example (preload on hover/focus):**
+
+```tsx
+function EditorButton({ onClick }: { onClick: () => void }) {
+  const preload = () => {
+    if (typeof window !== "undefined") {
+      void import("./monaco-editor");
+    }
+  };
+
+  return (
+    <button onMouseEnter={preload} onFocus={preload} onClick={onClick}>
+      Open Editor
+    </button>
+  );
+}
+```
+
+**Example (preload when feature flag is enabled):**
+
+```tsx
+function FlagsProvider({ children, flags }: Props) {
+  useEffect(() => {
+    if (flags.editorEnabled && typeof window !== "undefined") {
+      void import("./monaco-editor").then((mod) => mod.init());
+    }
+  }, [flags.editorEnabled]);
+
+  return <FlagsContext.Provider value={flags}>{children}</FlagsContext.Provider>;
+}
+```
+
+The `typeof window !== 'undefined'` check prevents bundling preloaded modules for SSR, optimizing server bundle size and build speed.