WIP: Fill in some of the 'load scenario' tests

src/index.js

@@ -280,16 +280,21 @@ document.querySelector('#upload-save').addEventListener('click', () => {
 
 document.querySelector('input[type="file"]').addEventListener('change', e => {
   const [file] =  fileInputEl.files;
+  const reader = new FileReader();
 
-
-  let reader = new FileReader();
   reader.onload = function () {
     const parser = new DOMParser();
     const doc = parser.parseFromString(reader.result, "image/svg+xml");
 
-    buildScenario(doc);
+    mapResourceEl.addEventListener(
+      'transitionend',
+      () => buildScenario(doc),
+      { once: true }
+    );
   };
 
+  mapPlaceholder.style.opacity = 1;
+  mapResourceEl.style.opacity = 0;
   reader.readAsText(file);
 });