I've mentioned this in #552 (comment), but I've confirmed it happens in 1.8 only now.

I've investigated it and found the root cause.

It happens with GopherJS 1.8-wip only when "os" package is imported (not necessarily directly). That package is often imported by other packages, such as "net/http", or if you're getting os.Stdout, etc.

It happens because of Executable() addition to os package in Go 1.8.

As a result, os.Getwd() gets called as part of os package initialization:

var initCwd, initCwdErr = Getwd()

Source: https://github.com/golang/go/blob/09762ccff79ebf08839f8954ab99c17d41f071e2/src/os/executable_darwin.go#L9.

Calling os.Getwd() in browser ends up making a call to Syscall, which causes the warning to get printed to console (note that it's actually printed as an error to console).