Command+DELETE no longer working on Hammerspoon once the app focus switches to another

Question

I'm now writing my own init.lua on Hammerspoon, and would like to remap some of my kews to others. Specifically, I would like to switch backslash key and delete key on my macOS.

However, while the simple delete and backslash works properly, once I switch my app focus to another, type in something there, and go back to the original app, the delete key (actually backslash key as I switched it) gets longer working; instead it deletes the characters in the app before it aborts the focus (i.e. the second to last focused app). But if I type in something there and then try again to delete it, suddenly the deletion works again without any problems.

I wonder why it is suddenly not working; it might be a bug, though. Anyway here is my init.lua to switch delete and backslash.

local VK_BACKSLASH = 0x2a
local VK_DELETE = 0x33
keyEventtap = hs.eventtap.new({
    hs.eventtap.event.types.keyDown
}, function(event)
    local bundleId = string.lower(hs.application.frontmostApplication():bundleID())
    local keyCode = event:getKeyCode()
    local flags = event:getFlags()

    if keyCode == VK_DELETE then
        if flagsMatches(flags, {'shift'}) then
            event:setKeyCode(VK_BACKSLASH)
            event:setFlags({shift=true})
        else
            event:setKeyCode(VK_BACKSLASH)
        end
    elseif keyCode == VK_BACKSLASH then
       event:setKeyCode(VK_DELETE) 
    end
end)

keyEventtap:start()

What am I missing here...?

Answer 1

You must add keyUp and flagsChanged event to monitor the event tap. So, instead of:

keyEventtap = hs.eventtap.new({
    hs.eventtap.event.types.keyDown
}, function(event)

change to the following:

keyEventtap = hs.eventtap.new({
    hs.eventtap.event.types.keyDown,
    hs.eventtap.event.types.flagsChanged,
    hs.eventtap.event.types.keyUp
}, function(event)

At least now this is working for me.