Google Appscript Web App receiving message from Chrome Extension-CodePudding

I am developing a web app on App Script (to use Google APIs). I have a chrome extension that works alongside the web app so that I can send information about the browser.

I am using a content script that initializes once the Web App loads. I want to simply send a message from the extension to the web app through the content script. However, DOM doesn't work because App Script uses iFrames. Here is the code from my actual web app:

<!DOCTYPE html>
<html>
  <head>
    <base target="_top">
  </head>
  <body>
    <input type="text" id="pageId" onchange="updateSessionInfo()">
  </body>
  <script>
    function updateSessionInfo(){
      var pageId = document.getElementById("pageId").value;
      google.script.run.update(pageId);
    }
  </script>
</html>

I was trying to use DOM to send the pageId to the input element and by having a change in the value, the update function would send the information.

However, this is the structure I receive on my browser:

Chrome Dev Tools

Am I thinking correctly? Or is editing the DOM both dirty and unfeasible? Is there another way?

UPDATE:

I have found the actual document HTML elements by looking deeper down the tree:

New Console

But if the element with id="pageId" is down there, why does it return null when I call it?

UPDATE:

I noticed times when it returns null, and sometimes where the element is detected:

Newest Console

CodePudding user response：

This works for me as a dialog:

Typically I would expect that if this will run as a dialog it will also run as a webapp with the addition of a doget();

gs:

function runmydialog() {
  const ui = SpreadsheetApp.getUi();
  ui.showModelessDialog(HtmlService.createHtmlOutputFromFile('ah2'),'test');
}

function update(msg) {
  SpreadsheetApp.getUi().alert(msg);
}

html:

<!DOCTYPE html>
<html>
 <head>
   <base target="_top">
</head>
<body>
  <body>
    <input type="text" id="pageId" onchange="updateSessionInfo()">
  <script>
    function updateSessionInfo(){
      var pageId = document.getElementById("pageId").value;
      google.script.run.update(pageId);
    }
  </script>
</body>
</html>

Dialog:

Alert:

I noticed that your script is not inside the body. I don't know if that makes a difference.