diff --git a/extensions-builtin/prompt-bracket-checker/javascript/prompt-bracket-checker.js b/extensions-builtin/prompt-bracket-checker/javascript/prompt-bracket-checker.js
index eccfb0f9..251a1f57 100644
--- a/extensions-builtin/prompt-bracket-checker/javascript/prompt-bracket-checker.js
+++ b/extensions-builtin/prompt-bracket-checker/javascript/prompt-bracket-checker.js
@@ -93,10 +93,12 @@ function checkBrackets(evt) {
 }
 
 var shadowRootLoaded = setInterval(function() {
-  var shadowTextArea = document.querySelector('gradio-app').shadowRoot.querySelectorAll('#txt2img_prompt > label > textarea');
-  if(shadowTextArea.length < 1) {
-      return false;
-  }
+  var sahdowRoot = document.querySelector('gradio-app').shadowRoot;
+  if(! sahdowRoot)  return false;
+
+  var shadowTextArea = sahdowRoot.querySelectorAll('#txt2img_prompt > label > textarea');
+  if(shadowTextArea.length < 1)  return false;
+
 
   clearInterval(shadowRootLoaded);
 
diff --git a/javascript/progressbar.js b/javascript/progressbar.js
index 18c771a2..2514d2e2 100644
--- a/javascript/progressbar.js
+++ b/javascript/progressbar.js
@@ -81,8 +81,13 @@ function request(url, data, handler, errorHandler){
     xhr.onreadystatechange = function () {
         if (xhr.readyState === 4) {
             if (xhr.status === 200) {
-                var js = JSON.parse(xhr.responseText);
-                handler(js)
+                try {
+                    var js = JSON.parse(xhr.responseText);
+                    handler(js)
+                } catch (error) {
+                    console.error(error);
+                    errorHandler()
+                }
             } else{
                 errorHandler()
             }