Javascript in a framed asset can no longer alter the DOM of the hosting page; here our asset attempts to add a green border around the frame. Because the frame is sandboxed, the browser will enforce security limits.
//wiki.ralfbarkow.ch/assets/framed/frame.html
framed
//misty-landmine.glitch.me/?load=examples/Wheel+Diagram.json&fullScreen=1&viewOnly=1&editLink=1®ionOfInterest={"x":[-6,6],"y":[-1,3]}
This diagram from Apparatus 
is hosted at glitch.com with some basic CORS headers.
# Web Messaging
The accepted standards based way to message between frames, windows, web components, wasm components and browser tabs is to use Web Messaging (ie window.postmessage).
I have proposed using something like Micro Frontends to create an alternative viewer for federation json. It is about time to revisit the Coordinated Viewing experiment we did a couple of years ago, where we managed to control Pretty Wiki using bi-dectional window.postmessage events/
# See also