Fix flicker of undefined

components/file-group-page.js

@@ -57,6 +57,8 @@ export class FileGroupPage extends HTMLElement {
     super()
     this.attachShadow({mode: 'open'})
     this.csp = "default-src 'self' 'unsafe-inline' 'unsafe-eval'"
+    this.viewLoaded = false
+    this.onceOnLoaded = undefined
   }
 
   connectedCallback() {
@@ -136,7 +138,11 @@ export class FileGroupPage extends HTMLElement {
       frame.srcdoc = frameHtml
     }
     frame.addEventListener('load', () => {
-      this.displayView()
+      this.viewLoaded = true
+      if (this.onceOnLoaded) {
+        this.onceOnLoaded()
+        this.onceOnLoaded = undefined
+      }
     })
     this.viewFrame = frame
     this.shadowRoot.append(frame)
@@ -144,9 +150,17 @@ export class FileGroupPage extends HTMLElement {
 
   displayView(doc) {
     const msg = ['srcdoc', doc]
-    this.viewFrame.contentWindow.postMessage(
-      msg, '*'
-    )
+    if (this.viewLoaded) {
+      this.viewFrame.contentWindow.postMessage(
+        msg, '*'
+      )
+    } else {
+      this.onceOnLoaded = () => {
+        this.viewFrame.contentWindow.postMessage(
+          msg, '*'
+        )
+      }
+    }
   }
 
   async displayEdit() {