Javascript has the benefit of being able to easily run natively on the web. Lua is more complex to get running in a browser, as other languages are as well.
Javascript has the disadvantage in that some people know and love and feel more comfortable in other languages. If you can convert from a language you love to a language that makes it easy to get into a browser... that's the dream.
Yup, that's my case, i miss the easy workflow of other languages with "more feature". I miss native namespace and packaging, class, a code completion that works... etc