Lua is famously easy to embed. Some implementations are fast as hell. It's comparatively a very rational and minimal language. It doesn't have to immediately interact with Javascript objects in any interesting way.
Please just embed the damn thing in a browser already. It's been way too long without any competiton to Javascript being allowed.
A lot of people want their language embedded in the browser suh as Lua, Dart, Ruby, etc.
But the way things are standing now it's not gonna happen. JavaScript, for the better and worse, is what we are stuck with. No browser vendor will be able to push though another language, and no standards committee would suggest a second scripting language to the web that runs alongside JavaScript.
If you absolutely cannot stand programming in JavaScript, which is the only native option for the web, you have to make do with the "language written on top of another language" solutions that are so popular these days, along with it's somewhat costy overhead.
The only real option is presumably the Dart route: Work really hard to make it compile to fast javascript and integrate well, and do a native VM as a separate option that can at some point be slotted in as an "optimisation" if the language gets enough traction. I don't think that alternative looks that bad. I'd rather have that, than go back to plugin hell or have browsers bloated with support for tons of languages.
Please just embed the damn thing in a browser already. It's been way too long without any competiton to Javascript being allowed.