Improves argument handling and script loading

assets/loader.js

@@ -0,0 +1,18 @@
+var openfreemapModuleUrl;
+var openfreemapStyleUrl;
+
+if (document.querySelector('.openfreemap') && typeof openfreemapModuleUrl === 'string') {
+  if (typeof openfreemapStyleUrl === 'string') {
+    var link = document.createElement('link');
+    link.rel = 'stylesheet';
+    link.href = openfreemapStyleUrl;
+    link.onerror = function () {
+      console.error('[OpenFreeMap] Failed to load the map stylesheet.');
+    };
+    document.head.appendChild(link);
+  }
+
+  import(openfreemapModuleUrl).catch(function (error) {
+    console.error('[OpenFreeMap] Failed to load the map library.', error);
+  });
+}