To overcome the lagging caused by naive mapping inoremap jk <ESC>. I have written a plugin called better-escape.vim. Here is how to use it:
let g:better_escape_shortcut = 'jk'
let g:better_escape_interval = 200
By default, the time interval threshold for the pressing of j and k is set to 150 ms. That is, if the time interval between pressing k and ...