refactored code and added win/lose popups

src/js/levels.js

@@ -0,0 +1,18 @@
+const cache=Object.create(null);
+
+const get=async filename => {
+	if(cache[filename]) return cache[filename];
+	const req=await fetch('levels/'+filename);
+	const json=await req.json();
+	return cache[filename]=json;
+};
+
+const clearCache=() =>
+	Object
+		.keys(cache)
+		.forEach(key => delete cache[key]);
+
+return module.exports={
+	get,
+	clearCache
+};