init.lua

-- https://github.com/Hammerspoon/hammerspoon/issues/664
slack_c_n = hs.hotkey.new({"ctrl"}, 'n', function()
      hs.eventtap.keyStroke({}, 'down')
  end)

slack_c_p = hs.hotkey.new({"ctrl"}, 'p', function()
      hs.eventtap.keyStroke({}, 'up')
  end)

hs.window.filter.new('Slack')
    :subscribe(hs.window.filter.windowFocused,function() slack_c_n:enable() end)
    :subscribe(hs.window.filter.windowUnfocused,function() slack_c_n:disable() end)

hs.window.filter.new('Slack')
    :subscribe(hs.window.filter.windowFocused,function() slack_c_p:enable() end)
    :subscribe(hs.window.filter.windowUnfocused,function() slack_c_p:disable() end)