feat: add warm-up script function to fetch resources before injection

Author: TheodoreRed

packages/web/src/generic.ts

@@ -3,6 +3,18 @@ import { initQueue } from './queue';
 import type { SpeedInsightsProps } from './types';
 import { computeRoute, getScriptSrc, isBrowser, isDevelopment } from './utils';
 
+/**
+ * Triggers a fetch call to the specified URL to warm up the endpoint.
+ * Any errors are silently ignored.
+ */
+async function warmUpScript(src: string): Promise<void> {
+  try {
+    await fetch(src);
+  } catch (err) {
+    void 0; // no-op to satisfy non-empty block rules
+  }
+}
+
 /**
  * Injects the Vercel Speed Insights script into the page head and starts tracking page views. Read more in our [documentation](https://vercel.com/docs/speed-insights).
  * @param [props] - Speed Insights options.
@@ -65,7 +77,9 @@ function injectSpeedInsights(
     );
   };
 
-  document.head.appendChild(script);
+  void warmUpScript(src).finally(() => {
+    document.head.appendChild(script);
+  });
 
   return {
     setRoute: (route: string | null): void => {