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

title, impact, impactDescription, tags

title	impact	impactDescription	tags
Preload Based on User Intent	MEDIUM	reduces perceived latency	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):

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):

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.