Scratch.vim

" A command that creates a scratch buffer.
"
" A scratch buffer is an unlisted buffer that is not assigned to a file,
" and will be wiped out as soon as you're out of it.
"
" 1. Opens a scratch buffer in a new window.
" 2. With a bang (:Scratch!) opens it in the same window.
" 3. Accepts arguments (:Scratch ft=javascript).
" 4. It auto-completes the arguments.

function! Scratch(bang, options) abort
  if a:bang
    let l:command = ':enew'
  else
    let l:command = ':new'
  endif
  let l:command .= ' | setlocal buftype=nofile bufhidden=wipe nobuflisted'
  if len(a:options) > 0
    let l:command .= ' ' . a:options
  endif
  execute 'silent ' . l:command
endfunction

command! -bang -nargs=* -complete=option Scratch call Scratch(<bang>0, <q-args>)