*I should've shared this a long time ago but better late than never....* Last winter, I was dealing with some confusion surrounding `iframe` sandboxing [when I wasn't aware it existed] on code playground sites (JSFiddle, JSBin, CodePen, etc.).
While investigating, I ended up creating a JS library called *sandblaster*  to assist me in analyzing *aaaaand* potentially modifying/dismantling iframe sandboxes. You can see a live analysis result example on its demo page . Please check it out if you're interested in the subject and feel free to contribute issues/PRs/tests/suggestions/etc. on its GitHub repo . Thanks! : https://github.com/JamesMGreene/sandblaster : http://jamesmgreene.github.io/sandblaster/test-iframes.html Sincerely, James Greene