How to create a key mapping to save file in any mode?

Question

I want to define <C-s> to save current editing file in any mode.
map <C-s> :call StripWhitespace()<CR> works fine in normal mode. But if I'm in insert mode, always need to Esc before saving.

Tried below methods, but failed.
imap <C-s> :call StripWhitespace()<CR>

function! My_Force_Save()
   if mode() != 'n'
      exe "normal! \<esc>"
   endif
   call StripWhitespace()
endfunction

---

function! StripWhitespace ()
    let save_cursor = getpos(".")
    let old_query = getreg('/')
    :%s/\s\+$//e
    call setpos('.', save_cursor)
    call setreg('/', old_query)
    exe ":w!"
endfunction

Answer 1

The :map command you tried works in normal, visual, and operator pending modes, and the :imap command works in insert mode, so you're going to need both, but you're also going to need to make a few changes.

Firstly, you should always use the non-recursive nore forms of the various map commands unless you have a specific reason not to.

Next, note that the map commands work as though you are typing out the things you map to. When you type a colon in visual mode, the command-line is pre-populated with a :'<,'> range. We don't want to pass this range to the :call command, so we need to clear it first with Ctrl-U:

noremap <C-S> :<C-U>call StripWhitespace()<CR>

Similarly, to call a function from an insert mode map, you need to include the Esc in your mapping:

inoremap <C-S> <Esc>:call StripWhitespace()<CR>

Even better, use Ctrl-O to perform a single command and remain in insert mode:

inoremap <C-S> <C-O>:call StripWhitespace()<CR>

See :help i_CTRL-O