fix(sdk,client): initialize crossframe observers after window load event

pkg/sdk/client/src/crossframe-messenger.ts

@@ -17,11 +17,10 @@ export class CrossFrameMessenger extends EventTarget {
         super()
         this.debug = false;
 
-        this._initResizeObserver();
-        this._initTitleMutationObserver();
-
         this._handleWindowMessage = this._handleWindowMessage.bind(this);
+        this._initObservers = this._initObservers.bind(this);
 
+        window.addEventListener('load', this._initObservers);
         window.addEventListener('message', this._handleWindowMessage)
     }
 
@@ -46,6 +45,11 @@ export class CrossFrameMessenger extends EventTarget {
         this.dispatchEvent(event);
     }
 
+    _initObservers() {
+        this._initResizeObserver();
+        this._initTitleMutationObserver();
+    }
+
     _initTitleMutationObserver() {
         const titleObserver = new MutationObserver((mutations) => {
             const title = mutations[0].target.textContent;
@@ -75,6 +79,10 @@ export class CrossFrameMessenger extends EventTarget {
             this.post({ type: CrossFrameMessageType.SIZE_CHANGED, data: { height, width }});
         });
 
-        resizeObserver.observe(document.body);
+        const body = document.body;
+
+        if (!body) return;
+
+        resizeObserver.observe(body);
     }
 }