Toggle major mode with a custom key binding

Question

I currently have 2 key bindings for switching between two major modes:

(global-set-key (kbd "<f12>") 'js2-jsx-mode)
(global-set-key (kbd "<f13>") 'web-mode)

How would I reduce that to a single key binding, so that it toggles between these modes depending on the current mode?

Answer 1

You can use the variable major-mode to find out the current Major Mode. The value is a Symbol, thus you can compare it using eq.

(defun toggle-between-web-mode-and-js2-jsx-mode ()
  (interactive)
  (cond ((eq major-mode 'web-mode) (js2-jsx-mode))
        ((eq major-mode 'js2-jsx-mode) (web-mode))))

(interactive) is required to make the function as an Emacs command, so you can bind some key to it.