Fix no previewer for no-code demos

Author: theCapypara

src/window.js

@@ -339,8 +339,10 @@ export default function Window({ application, session }) {
 
     const lang = langs[language.toLowerCase()];
     // Do nothing if there is no code to avoid compile errors
+    // unless the language is JavaScript, because in this case
+    // this is probably a demo without code.
     const text = lang.document.code_view.buffer.text.trim();
-    if (text === "") {
+    if (text === "" && language !== "JavaScript") {
       return;
     }