QUESTION: How to add javascript in the html without sanitization?

I tried adding the script to the iframe in which the canvas renders by adding a <script> tag at the end of the body of the iframe. This works to some extent. The problem here is that when I need to update the js inside the script I will need to refresh the iframe (to remove any event listeners if present) and doing so gives me the following error:

Can you provide a reproducible demo of your issue, please?

Thanks for the reply @artf. I was doing a mistake while updating the iframe so now my problem is solved! Just another question, is there any built-in method to refresh the iframe?