How to open or close NERDTree and Tagbar with <leader>\?

I want <leader>\ to open or close NERDTree and Tagbar, under the following conditions:

1. Only close both if NERDTree and Tagbar are both opened
2. Open both if NERDTree and Tagbar are closed OR if one is already opened

So far, in VIMRC, I have:

nmap <leader>\ :NERDTreeToggle<CR> :TagbarToggle<CR>

Which doesn't exactly work, since if one is opened, and the other closed. It would open the one that was closed and close the one that was opened.

How can this be achieved?

You need to use a function that checks whether the plugin windows are open or not and then acts accordingly. This should work and will also jump back to the window that you started in:

function! ToggleNERDTreeAndTagbar()
    let w:jumpbacktohere = 1

    " Detect which plugins are open
    if exists('t:NERDTreeBufName')
        let nerdtree_open = bufwinnr(t:NERDTreeBufName) != -1
    else
        let nerdtree_open = 0
    endif
    let tagbar_open = bufwinnr('__Tagbar__') != -1

    " Perform the appropriate action
    if nerdtree_open && tagbar_open
        NERDTreeClose
        TagbarClose
    elseif nerdtree_open
        TagbarOpen
    elseif tagbar_open
        NERDTree
    else
        NERDTree
        TagbarOpen
    endif

    " Jump back to the original window
    for window in range(1, winnr('$'))
        execute window . 'wincmd w'
        if exists('w:jumpbacktohere')
            unlet w:jumpbacktohere
            break
        endif
    endfor
endfunction
nnoremap <leader>\ :call ToggleNERDTreeAndTagbar()<CR>