index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>HTML 5 Boilerplate</title>
    <link rel="stylesheet" href="style.css">
  </head>
  <body>
    <h2>Simulated VerunaDocs Webpage</h2>
    <button id="veruna_button">Click to Open Email</button>
    <script type="text/javascript">
          var anchorLink = document.getElementById('veruna_button').addEventListener("click", function(event) {

          const queryString = window.location.search;
          const urlParams = new URLSearchParams(queryString);
            
          var emailJson = {
            "action": "showEmailComposer",
            "username": urlParams.get('username'),
            "ObjectId": urlParams.get('ObjectId'),
            "ObjectType": urlParams.get('ObjectType'),
            "AccountName": urlParams.get('AccountName'),
            "AccountId": urlParams.get('AccountId'),
            "SessionId": "dummyParam",
            "OrgId": urlParams.get('OrgId'),
            "SFTheme": "Theme3",
            "selectedFileIds": [
              "5a7bf8a6-94d8-43d4-bbbc-d79b00c615b0",
              "8af6b93f-2497-4de3-9561-d75730d92d20",
              "7bd47364-53ec-4890-a110-9b1b405f6f5d"
            ]
          };
          
          window.parent.postMessage(emailJson, "*");
          window.postMessage(emailJson, "*");
        });        
    </script>
  </body>
</html>