How do I write vimrc configuration that works in both Vim and Neovim by detecting which one is running?

Explanation

The has() function tests whether a feature or capability is available, returning 1 (true) or 0 (false). It is the standard tool for writing portable .vimrc / init.vim configuration that adapts to different Vim versions, platforms, and compiled features — including detecting Neovim.

How it works

has({feature}) accepts a feature name and returns 1 if available. Common guards:

• has('nvim') — running in Neovim
• has('python3') — Python 3 support compiled in
• has('job') — async job control (Vim 8+)
• has('timers') — timer support (Vim 8+)
• has('patch-8.2.4919') — specific Vim patch level
• has('unix') / has('win32') — OS platform
• has('gui_running') — inside a GUI (gVim, MacVim)

Example

Apply settings specific to each editor:

if has('nvim')
  " Neovim-only: live preview of substitutions
  set inccommand=split
  tnoremap <Esc> <C-\><C-n>
else
  " Vim 8-only: built-in terminal size
  set termwinsize=12x0
endif

Guard against missing features before using them:

if has('timers')
  call timer_start(500, {-> execute('checktime')})
endif

if has('patch-9.0.0185')
  set smoothscroll
endif

Tips

• Test any feature string interactively: :echo has('nvim')
• Full list of valid feature names: :help feature-list
• For precise version checks, has('patch-X.Y.Z') is more reliable than comparing v:version directly