diff --git a/client/commonFramework/end.js b/client/commonFramework/end.js
index 323b0d41f9..c0cd76129d 100644
--- a/client/commonFramework/end.js
+++ b/client/commonFramework/end.js
@@ -7,12 +7,15 @@ $(document).ready(function() {
     init($);
   });
 
-  common.editorKeyUp$
+  const code$ = common.editorKeyUp$
     .debounce(750)
     .map(() => common.editor.getValue())
     .distinctUntilChanged()
     .doOnNext(() => console.log('updating value'))
-    .subscribe(
+    .shareReplay();
+
+  // update storage
+  code$.subscribe(
       code => {
         common.codeStorage.updateStorage(common.challengeName, code);
         common.codeUri.querify(code);
@@ -20,6 +23,28 @@ $(document).ready(function() {
       err => console.error(err)
     );
 
+  code$
+    .flatMap(code => {
+      if (common.hasJs(code)) {
+        return common.detectLoops$(code)
+          .flatMap(
+            ({ err }) => err ? Observable.throw(err) : Observable.just(code)
+          );
+      }
+      return Observable.just(code);
+    })
+    .flatMap(code => common.updatePreview$(code))
+    .catch(err => Observable.just({ err }))
+    .subscribe(
+      ({ err }) => {
+        if (err) {
+          return console.error(err);
+        }
+        console.log('updating preview');
+      },
+      err => console.error(err)
+    );
+
   common.resetBtn$
     .doOnNext(() => {
       common.editor.setValue(common.replaceSafeTags(common.seed));
diff --git a/client/commonFramework/execute-challenge-stream.js b/client/commonFramework/execute-challenge-stream.js
index 57196e2312..86541bbb70 100644
--- a/client/commonFramework/execute-challenge-stream.js
+++ b/client/commonFramework/execute-challenge-stream.js
@@ -60,20 +60,6 @@ window.common = (function(global) {
           });
         }
 
-        if (common.challengeType === '0') {
-          let openingComments = code.match(/\<\!\-\-/gi);
-          let closingComments = code.match(/\-\-\>/gi) || [];
-          if (
-            openingComments &&
-            openingComments.length > closingComments.length
-          ) {
-            return Observable.throw({
-              err: 'SyntaxError: Unfinished HTML comment',
-              code
-            });
-          }
-        }
-
         if (code.match(detectUnsafeConsoleCall)) {
           return Observable.throw({
             err: 'Invalid if (null) console.log(1); detected',
diff --git a/client/commonFramework/update-preview.js b/client/commonFramework/update-preview.js
index 09af6725fa..e8acb518d7 100644
--- a/client/commonFramework/update-preview.js
+++ b/client/commonFramework/update-preview.js
@@ -43,7 +43,7 @@ window.common = (function(global) {
       .map(script => `<script>${script}</script>`)
       .flatMap(script => {
         preview.open();
-        preview.write(libraryIncludes + code + script);
+        preview.write(libraryIncludes + code + '<!-- -->' + script);
         preview.close();
         return Observable.fromCallback($(preview).ready, $(preview))()
           .first()