Author here. We have experimented with Realms in the past and had a working version for some time. Also did some POC with quickjs. In both scenarios, we saw performance degrade a lot.. So our current eval is run actually in the web worker so we take extra precautions to avoid leaking any problem some browser api inside the eval context. I like the idea of having a wasm eval environment as well, will experiment with that soon. Thanks for the tips :)