Yeah, it's possible to install v8 or spidermonkey shells and use them to run code - we use them to run parts of the .NET wasm test suite - but they have a bunch of arbitrary limitations, so if you're trying to emulate a browser I'm not sure I'd bet on them. It's certainly going to be easier than a C++ embedding, so it makes sense that they took that route.
Another option is to use node, but it also has weird limitations/behaviors when running code.
Another option is to use node, but it also has weird limitations/behaviors when running code.