In evil-mode how to just press J to move the cursor down 3 lines

Question

When in evil-mode, I can make the cursor go down 3 lines by command 'C-u 3 M-x evil-next-line' , but how can I make the cursor go down 3 lines by just pressing J?

Answer 1

1. Short answer

Add this to your .emacs file:

(evil-define-motion evil-next-line-3 (count)
  "Move the cursor 3 * COUNT lines down."
  :type line
  (let (line-move-visual)
    (evil-line-move (* 3 (or count 1)))))

Note that J is currently bound to evil-join.

If you are ok to rebind it, just add:

(define-key evil-normal-state-map "J" 'evil-next-line-3)

Now, to join lines, you may either type M-x evil-join RET or bind something else to evil-join (see below).

Note that, if you type 2J, you'll move twice 3 lines down, which is more or less 6 lines down... and C-u J will move 4*3 = 12 lines down.

2. Not so short answer (what I actually did)

I never used evil-mode... so I tried to add this package and enabled the evil-mode (which is ok for me since I know the main vi commands and I know how to disable it with C-- M-x evil-mode RET).

When evil-mode is enabled and I type C-h k J, the Help buffer says:

J runs the command evil-join (found in evil-normal-state-map), 
which is an interactive compiled Lisp function in ‘evil-commands.el’.

It is bound to J.

(evil-join BEG END)

Join the selected lines.

Then I typed C-h k j, clicked the evil-commands.el link from the Help buffer and copied and adapted the definition of the evil-next-line function to the evil-next-line-3 function and bound it to J.

In case you want to go back to the previous binding of J (or want to bind it to something else), you can evaluate something like:

(define-key evil-normal-state-map "J" 'evil-join)