My keybindings for Inkdrop's vim plugin

keymap.cson

{
  ".CodeMirror.vim-mode": {},
  ".CodeMirror.vim-mode.normal-mode textarea": {
    "escape": "vim:reset-normal-mode"
  },
  ".CodeMirror.vim-mode:not(.insert-mode):not(.key-buffering) textarea": {
    "h": "vim:move-left",
    "left": "vim:move-left",
    "backspace": "vim:move-left",
    "l": "vim:move-right",
    "right": "vim:move-right",
    "space": "vim:move-right",
    "k": "vim:move-up",
    "up": "vim:move-up",
    "j": "vim:move-down",
    "down": "vim:move-down",
    "g k": "vim:move-up-by-display-lines",
    "g j": "vim:move-down-by-display-lines",

    "w": "vim:move-to-next-word",
    "W": "vim:move-to-next-whole-word",
    "e": "vim:move-to-end-of-word",
    "g e": "vim:move-to-previous-end-of-word",
    "E": "vim:move-to-end-of-whole-word",
    "g E": "vim:move-to-previous-end-of-whole-word",
    "b": "vim:move-to-previous-word",
    "B": "vim:move-to-previous-whole-word",
    "}": "vim:move-to-next-paragraph",
    "{": "vim:move-to-previous-paragraph",
    "|": "vim:move-to-beginning-of-line",
    "0": "vim:move-to-beginning-of-line-with-zero",
    "^": "vim:move-to-first-character-of-line",
    "_": "vim:move-to-first-character-of-line-and-down",
    "$": "vim:move-to-last-character-of-line",
    "g _": "vim:move-to-last-nonblank-character-of-line-and-down",
    "-": "vim:move-to-first-character-of-line-up",
    "+": "vim:move-to-first-character-of-line-down",
    "enter": "vim:move-to-first-character-of-line-down",
    "g g": "vim:move-to-start-of-file",
    "ctrl-u": "vim:scroll-half-screen-up",
    "ctrl-b": "vim:scroll-full-screen-up",
    "ctrl-d": "vim:scroll-half-screen-down",
    "ctrl-f": "vim:scroll-full-screen-down",
    "ctrl-e": "vim:scroll-down",
    "ctrl-y": "vim:scroll-up",
    "z enter": "vim:scroll-cursor-to-top",
    "z t": "vim:scroll-cursor-to-top-leave",
    "z .": "vim:scroll-cursor-to-middle",
    "z z": "vim:scroll-cursor-to-middle-leave",
    "z -": "vim:scroll-cursor-to-bottom",
    "z b": "vim:scroll-cursor-to-bottom-leave",
    "z s": "vim:scroll-cursor-to-left",
    "z e": "vim:scroll-cursor-to-right",
    "z M": "editor:fold-all",
    "z R": "editor:unfold-all",
    "z c": "editor:fold-current-row",
    "z o": "editor:unfold-current-row",
    "G": "vim:move-to-line",
    "H": "vim:move-to-top-of-screen",
    "L": "vim:move-to-bottom-of-screen",
    "M": "vim:move-to-middle-of-screen",

    "d": "vim:delete",
    "D": "vim:delete-to-last-character-of-line",
    "c": "vim:change",
    "C": "vim:change-to-last-character-of-line",
    "r": "vim:replace",
    ">": "vim:indent",
    "<": "vim:outdent",
    "=": "vim:auto-indent",
    "J": "vim:join",

    "y": "vim:yank",
    "Y": "vim:yank-line",
    "P": "vim:put-before",
    "p": "vim:put-after",

    "g ~": "vim:toggle-case",
    "g U": "vim:upper-case",
    "g u": "vim:lower-case",
    "~": "vim:toggle-case-now",

    "m": "vim:mark",
    "`": "vim:move-to-mark-literal",
    "'": "vim:move-to-mark",

    "f": "vim:find",
    "F": "vim:find-backwards",
    "t": "vim:till",
    "T": "vim:till-backwards",
    ";": "vim:repeat-find",
    ",": "vim:repeat-find-reverse",

    "/": "vim:search",
    "?": "vim:reverse-search",
    "*": "vim:search-current-word",
    "#": "vim:reverse-search-current-word",
    "n": "vim:repeat-search",
    "N": "vim:repeat-search-backwards",

    "%": "vim:bracket-matching-motion",

    ":": "vim:ex-command"
  },
  ".CodeMirror.vim-mode:not(.insert-mode):not(.key-buffering-command) textarea": {
    "i": "vim:text-object-manipulation-inner",
    "a": "vim:text-object-manipulation"
  },
  ".CodeMirror.vim-mode.normal-mode:not(.key-buffering):not(.visual-mode) textarea": {
    "i": "vim:activate-insert-mode",
    "I": "vim:insert-at-beginning-of-line",
    "insert": "vim:activate-insert-mode",
    "R": "vim:activate-replace-mode",
    "v": "vim:activate-characterwise-visual-mode",
    "V": "vim:activate-linewise-visual-mode",
    "ctrl-v": "vim:activate-blockwise-visual-mode",
    "ctrl-q": "vim:activate-blockwise-visual-mode",

    "u": "vim:undo",
    "ctrl-r": "core:redo",

    "O": "vim:insert-above-with-newline",
    "o": "vim:insert-below-with-newline",
    "a": "vim:insert-after",
    "A": "vim:insert-after-end-of-line",
    "x": "vim:delete-right",
    "X": "vim:delete-left",
    "s": "vim:substitute",
    "S": "vim:substitute-line",
    ".": "vim:repeat",

    "ctrl-a": "vim:increase",
    "ctrl-x": "vim:decrease",

    "\"": "vim:register-prefix"
  },
  ".CodeMirror.vim-mode.insert-mode textarea": {
    "escape": "vim:exit-insert-mode",
    "j j": "vim:exit-insert-mode",
    "ctrl-w": "vim:delete-to-beginning-of-word"
  },
  ".CodeMirror.vim-mode.replace-mode textarea": {
    "escape": "vim:exit-insert-mode"
  },
  ".CodeMirror.vim-mode.visual-mode textarea": {
    "escape": "vim:exit-visual-mode",
    "\"": "vim:register-prefix",
    "I": "vim:insert-at-start-of-target",
    "A": "vim:insert-at-end-of-target",
    "v": "vim:activate-characterwise-visual-mode",
    "V": "vim:activate-linewise-visual-mode",
    "o": "vim:reverse-selections",
    "O": "vim:reverse-selections-at-same-line",
    "x": "vim:delete-right",
    "X": "vim:delete-left",
    "s": "vim:substitute-visual",
    "S": "vim:substitute-line-visual"
  },
  ".note-list-bar": {
    "k": "core:open-prev-note",
    "j": "core:open-next-note"
  },
  ".mde-preview": {
    "g g": "vim:move-to-start-of-file",
    "ctrl-u": "vim:scroll-half-screen-up",
    "ctrl-b": "vim:scroll-full-screen-up",
    "ctrl-d": "vim:scroll-half-screen-down",
    "ctrl-f": "vim:scroll-full-screen-down",
    "k": "vim:scroll-up",
    "j": "vim:scroll-down",
    "G": "vim:move-to-line",
    "H": "vim:move-to-start-of-file"
  }
}

Curious as to how you made the following work:

   "j j": "vim-mode:exit-insert-mode",

It works for me, but disables all use of the 'j' key while in insert mode.

Sorry, I couldn't solve the problem and now ignore the custom command.
I also want to know the solution for it.