.dir-locals.el

((nil
  (eval progn
        (let
            ((base-path
              (locate-dominating-file default-directory ".dir-locals.el")))
          ;; Custom backup path
          ;; Or you can set `make-backup-files` to `nil`.
          (make-local-variable 'backup-directory-alist)
          (add-to-list 'backup-directory-alist
                       `(".*" \,
                         (expand-file-name ".backup" base-path)))
          ;; Custom exec path
          (make-local-variable 'exec-path)
          (add-to-list 'exec-path
                       (expand-file-name "node_modules/.bin/" base-path))))))