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You can use DOM manipulation API of javascript to do so.
We have implemented an iframe as an example (Github link given on top). You can click increaseSessionTime to make that iframe visible. Check the /js/eventHandler.js file in the demo code from Github.
Check the following links and examples:
https://www.w3schools.com/js/js_htmldom.asp
https://www.w3schools.com/jsref/met_document_createelement.asp
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