<script>
// add this script block to viewer.html (pdfjs/web/viewer.html)
document.addEventListener('DOMContentLoaded', function() {
console.log('DOMContentLoaded');
}, true);
document.addEventListener('webviewerloaded', function(e) {
console.log('webviewerloaded');
});
</script>
// you can put anywhere in viewer.js (pdfjs/web/viewer.js) and listens to it
const event = document.createEvent("CustomEvent");
event.initCustomEvent("your_new_event", true, true, {});
document.dispatchEvent(event);