realms-shim

Salesforce does this with a combination of web components, with a patched up ShadowRoot so that code with a reference to the shadow root can't walk into the rest of the document, and a secure evaluator function related to SES (Secure EcmaScript) to limit the globals the untrusted script has access too. The secure evaluator is wild. I think this is the heart of it: https://github.com/Agoric/realms-shim/blob/v1.1.0/src/evalua... There's also an idea for isolated web components to solve this in the platform: https://github.com/WICG/webcomponents/issues/1002

Ah, okay this is interesting. The entire notebook is one iframe, which lets you do more of the metaprogramming and sharing variables. Both printing (via console) and non-printing infinite loops crash the iframe until you close the page. And the reason my document.innerHTML = "" test was recoverable is that your notebook-top-button-container is not in the iframe (and it has that refresh button!). I'll have to look more into async stuff. Great eval article there. I've found these four lines to work for importing content[1]. I dove into realms[2] and the realms shim [3] a while ago after reading about Figma's engineering behind plugins [4] but I never figured out how I might use that for my system. You might take a look at how the codemirror author built his book [5] and editor [6] in this repo [7]. He implements the loop detection I derided

> web based programs that could allow third party add-ons The library in the current post, Seafox - cute name! - is "just" the parser, turning JavaScript code into an abstract syntax tree. One would need a sandboxed interpreter/evaluator/virtual machine to run it. You might be aware of Figma's efforts, where they compiled Fabrice Bellard's QuickJS engine (in C) to WASM, to use for their plugin system. https://www.figma.com/blog/how-we-built-the-figma-plugin-sys... https://www.figma.com/blog/an-update-on-plugin-security/ https://bellard.org/quickjs/ The first article describes an earlier system using Realms, a shim/polyfill for an ECMAScript proposal. https://github.com/agoric/realms-shim/ https://github.com/tc39/proposal-realms

Thanks. The "with(proxy)" part specifically would be mine. The old Google Caja, from the EcmaScript-5 days preceding Proxies, did something similar: https://github.com/google/caja/blob/master/src/com/google/ca... The full new pattern, combining "with(proxy)" with a clever use of direct "eval", is from Caridy Patino of Salesforce. The modern Realms Shim https://github.com/Agoric/realms-shim , and the SES Shim which builds on it https://github.com/Agoric/SES , is a collaboration of Agoric and Salesforce, especially JF Paradis of Salesforce. We have come to refer to the fragment of code with the "with(proxy)" and the direct "eval" as the "Eight magic lines of code" and "The heart of the shim". It is explained at https://www.youtube.com/watch?v=9Snbss_tawI&list=PLKr-mvz8uv... and https://www.youtube.com/watch?v=mSNxsn0pK74&list=PLKr-mvz8uv..