Add `j` and `k` shortcuts

app/assets/javascripts/shortcuts_issuable.coffee

@@ -16,12 +16,31 @@ class @ShortcutsIssuable extends ShortcutsNavigation
       @replyWithSelectedText()
       return false
     )
+    Mousetrap.bind('j', =>
+      @prevIssue()
+      return false
+    )
+    Mousetrap.bind('k', =>
+      @nextIssue()
+      return false
+    )
+
 
     if isMergeRequest
       @enabledHelp.push('.hidden-shortcut.merge_requests')
     else
       @enabledHelp.push('.hidden-shortcut.issues')
 
+  prevIssue: ->
+    $prevBtn = $('.prev-btn')
+    if not $prevBtn.hasClass('disabled')
+      Turbolinks.visit($prevBtn.attr('href'))
+
+  nextIssue: ->
+    $nextBtn = $('.next-btn')
+    if not $nextBtn.hasClass('disabled')
+      Turbolinks.visit($nextBtn.attr('href'))
+
   replyWithSelectedText: ->
     if window.getSelection
       selected = window.getSelection().toString()

app/views/shared/issuable/_sidebar.html.haml

@@ -13,12 +13,12 @@
             = icon('angle-double-right')
       .issuable-nav.pull-right.btn-group{role: 'group', "aria-label" => '...'}
         - if has_prev_issuable?(@project, issuable.id)
-          = link_to 'Prev', issuable_link_prev(@project, issuable), class: 'btn btn-default'
+          = link_to 'Prev', issuable_link_prev(@project, issuable), class: 'btn btn-default prev-btn'
         - else
           %a.btn.btn-default.disabled{href: '#'}
             Prev
         - if has_next_issuable?(@project, issuable.id)
-          = link_to 'Next', issuable_link_next(@project, issuable), class: 'btn btn-default'
+          = link_to 'Next', issuable_link_next(@project, issuable), class: 'btn btn-default next-btn'
         - else
           %a.btn.btn-default.disabled{href: '#'}
             Next