I just started playing with Go's WebAssembly support last night. Support is still nascent but I was able to get up and running very quickly, and the API is dead simple: https://github.com/golang/go/wiki/WebAssembly
https://github.com/aykevl/tinygo
It's output files are very small (~1kb for the toy examples), as it does dead code elimination, which is missing from the mainline Go approach (for now).
Both Go and TinyGo are in very early stages of their Wasm support though, so things are changing and updating fairly quickly. :)
For Wasm output? It really doesn't seem like it. Output binaries from the mainline Go compiler (atm) are ~2MB. Most of which is dead code.