feat: focus search input on page load (#815)

When a user opens [jsr.io](https://jsr.io), the page shows a big input
element which is used to search for packages. It appears to be the
primary call to action element and I believe by default, it should be
focused on page load because most of the times, a user would visit jsr
to search for a package.

This behaviour would also align with [google.com](https://google.com)

frontend/islands/GlobalSearch.tsx

@@ -9,7 +9,7 @@ import type { OramaPackageHit, SearchKind } from "../util.ts";
 import { api, path } from "../utils/api.ts";
 import type { List, Package, RuntimeCompat } from "../utils/api_types.ts";
 import { PackageHit } from "../components/PackageHit.tsx";
-import { useMacLike } from "../utils/os.ts";
+import { useIsMobileDevice, useMacLike } from "../utils/os.ts";
 import type { ListDisplayItem } from "../components/List.tsx";
 import { RUNTIME_COMPAT_KEYS } from "../components/RuntimeCompatIndicator.tsx";
 
@@ -55,6 +55,7 @@ export function GlobalSearch(
     isFocused.value && search.value.length > 0
   );
   const macLike = useMacLike();
+  const isMobileDevice = useIsMobileDevice();
 
   const orama = useMemo(() => {
     if (IS_BROWSER && indexId) {
@@ -65,6 +66,14 @@ export function GlobalSearch(
     }
   }, [indexId, apiKey]);
 
+  // focus the "search for packages" input box when the site loads
+  useEffect(() => {
+    if (location.pathname === "/" && !isMobileDevice) {
+      (document.querySelector("#global-search-input") as HTMLInputElement)
+        ?.focus();
+    }
+  }, []);
+
   useEffect(() => {
     const outsideClick = (e: Event) => {
       if (!ref.current) return;

frontend/utils/os.ts

@@ -6,3 +6,10 @@ export function useMacLike(): boolean | undefined {
   if (!IS_BROWSER) return undefined;
   return !!navigator.platform.match(/(Mac|iPhone|iPod|iPad)/i);
 }
+
+export function useIsMobileDevice(): boolean | undefined {
+  if (!IS_BROWSER) return undefined;
+  return !!navigator.userAgent.match(
+    /Android|webOS|iPhone|iPad|iPod|BlackBerry/i,
+  );
+}