If you are not very familiar with coffeescript you may want to know what it will look like when it is compiled to js. This is a simple script to help you do that in vim.
" Created compiled js file
function! s:Coffee2Js()
let current_coffee = expand('%')
let filename = substitute(expand('%:t'), ".coffee$", "", "")
exec('! coffee -co /tmp ' . current_coffee)
exec('split /tmp/' . filename . '.js')
endfunction
"
" Register a new command `C2J` for compile coffee to a js file
command! C2J :call <SID>Coffee2Js()
Now it is easy to check the js :)