You have to use web dev module and with python endpoint you can inject dynamic html js code into your widget and send it to client (iframe)
Also use Ajax to request tag value by polling or event base in your js code. For this, create another account python endpoint with your custom API to response to the tag value reguest from your js code.
Do the same for writing value from your js code.
I use this method with three.js lib for creating interactive 3d view.
For interactive with perspective view in your web dev API use system.perspective.sendmessage with specific session ID to pass Ajax request to your view.
By best advise is create module but it forces you to learn Java 
and type script and also react but the result is compact and easy to use for others.
You can also protect your code with module.