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Add renderMethodReady() using postMessage(). #15

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Add renderMethodReady() using postMessage(). #15

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742b3e3
Add renderMethodReady() using postMessage().
BigBlueHat May 19, 2026
62a35f6
Add Download PDF after iframe if provided.
BigBlueHat May 19, 2026
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29 changes: 29 additions & 0 deletions app.js
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Original file line number Diff line number Diff line change
Expand Up @@ -99,5 +99,34 @@ window.app = createApp({
},
loadExampleCredential(event) {
this.loadCredential(event.target.value);
},
setupMessaging(el) {
const iframe = el;
const loader = el.nextElementSibling;
// create a MessageChannel; transfer one port to the iframe
const channel = new MessageChannel();
// start message queue so messages won't be lost while iframe loads
channel.port1.start();
// handle `ready` message
channel.port1.onmessage = function(event) {
if(event.data?.ready) {
iframe.removeAttribute('hidden');
loader.setAttribute('hidden', 'hidden');
if(event.data?.pdf) {
// append another iframe after the current one with the PDF data URL
const pdfDownloadLink = document.createElement('a');
pdfDownloadLink.href = event.data.pdf;
pdfDownloadLink.download = 'credential.pdf';
pdfDownloadLink.textContent = 'Download PDF';
pdfDownloadLink.type = 'application/pdf';
iframe.insertAdjacentElement('afterend', pdfDownloadLink);
}
} else {
new Error(event.data?.error?.message);
}
channel.port1.onmessage = undefined;
};
// send "start" message; send `port2` to iframe for return communication
iframe.contentWindow.postMessage('start', '*', [channel.port2]);
}
}).mount();
8 changes: 7 additions & 1 deletion index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,13 @@
@click="currentTab = 'credential'">Filtered Credential</div>
</div>
<div class="ui bottom attached tab segment" :class="{ active: currentTab == 'rendered' }">
<iframe sandbox="allow-scripts allow-modals" :srcdoc="shimCode()" style="width: 100%; border: none;"></iframe>
<iframe sandbox="allow-scripts allow-modals"
hidden
:srcdoc="shimCode()"
@load="setupMessaging($el)"
style="width: 100%; border: none;"></iframe>
<!-- loader shown until the above iframe is ready -->
<div class="ui placeholder"><div class="image"></div></div>
</div>
<div class="ui bottom attached tab segment" :class="{ active: currentTab == 'code' }">
<div class="ui form">
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20 changes: 20 additions & 0 deletions viewers/html.js
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,26 @@ export function HTMLViewer({template, credential, pointers}) {
<head>
<meta http-equiv="content-security-policy" content="default-src data: 'unsafe-inline'">
<script name="credential" type="application/vc">${store.filteredCredential}</script>
<script>
// add promise that will resolve to the communication port from
// the parent window
const portPromise = new Promise(resolve => {
window.addEventListener('message', function start(event) {
if(event.data === 'start' && event.ports?.[0]) {
window.removeEventListener('message', start);
resolve(event.ports[0]);
}
});
});

// attach a function to the window for the template to call when
// it's "ready" (or that an error occurred) that will send a message
// to the parent so the parent can decide whether to show the iframe
window.renderMethodReady = function(resp) {
portPromise.then(port => port.postMessage(
!resp.error ? resp : {error: {message: resp.error.message}}));
};
Comment on lines +54 to +57

@dlongley dlongley May 19, 2026

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Maybe we'll want a different name than renderMethodReady if we're going to pass other things -- or at least, we don't want to have both {ready: true} and renderMethodReady as the names, it seems redundant. Maybe it's the {ready: true} that should change -- and passing any object at all is optional.

</script>
</head>
<body>
${store.code}
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