When our browser-based eID workflows are run in an HTML `iframe`, it is good to set up an event listener on the parent window, to get a JS-event notification when the login workflow is completed either with a success or an error. See [MDN Mozilla Developer Network – Window.postMessage()](https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage) The event.data contains an object as below, where `command` will always be set to ‘zignsec_postback’. ### Setup Eventlistener HTML and Javascript example: ```html <div id="event_response">Javascript Event Response: NOEVENT</div> <br> <div class="row"> <script type="text/javascript"> window.addEventListener("message", receiveMessage, false); function receiveMessage(event) { var response = event.data; document.getElementById('event_response').innerText = "Javascript Event Response: " + response; } </script> </div> ``` <br> <div class="row"> <script type="text/javascript"> window.addEventListener("message", receiveMessage, false); function receiveMessage(event) { var response = event.data; document.getElementById('event_response').innerText = "Javascript Event Response: " + response; } </script> </div> ### Event Data Returned on Cancelled Login Json example: ```json { "command":"zignsec_postback", "errorcode":"USER_CANCEL", "error":"Action cancelled", "token":"a54330cd-90dc-41f8-bcd5-22d87701d876" } ``` ### Event Data Returned on Successful Login Json example: ```json { "command":"zignsec_postback", "errorcode":"", "error":"", "token":"1decb781-37db-4477-92f8-223586dd4f0f" } ```