function! Handler(ch, msg) echom a:msg endfunction
let job = job_start('cmd /c dir /s/b c:', { 'callback': 'Handler' })
https://groups.google.com/d/msg/vim_dev/qtw5LdCrHJQ/uDhLZslb... https://github.com/vim/vim/commit/38a55639d603823efcf2d2fdf5...