Tutorial 7: Remembering Things: A Press Counter

Built from the _G persistence pattern already confirmed in Your First Menu — stripped down to just the state, with the menu removed, so the idea stands on its own before you add anything else to it.

Every OnKey script you’ve written so far re-runs its entire file from scratch on every press. Any plain local variable is created fresh and thrown away the instant the script finishes — there’s no memory between presses unless you deliberately build some. This tutorial builds the smallest possible piece of memory: a number that goes up by one each time you press a key.

The problem, first

Create scripts/OnKey/press_counter_broken.lua:

local KEYVAL = "insert"  -- must be in the first 10 lines

local nCount = 0
nCount = nCount + 1
Loader.Printf("[press_counter] count is now: " .. nCount)

Press Insert several times and check the log. Every single line says count is now: 1 — nCount starts over at 0 on every press, because local variables don’t survive past the end of the script that created them.

The fix: _G

_G is the one table that’s genuinely shared and kept alive across separate script runs. Create scripts/OnKey/press_counter.lua:

local KEYVAL = "insert"

_G.TutorialPressCount = (_G.TutorialPressCount or 0) + 1
Loader.Printf("[press_counter] count is now: " .. _G.TutorialPressCount)

Press Insert several times:

[press_counter] count is now: 1
[press_counter] count is now: 2
[press_counter] count is now: 3

[Image placeholder — ../img/presscounterlog.png] Screenshot of lua_loader_printf.log showing at least 4-5 consecutive [press_counter] count is now: N lines with N genuinely incrementing each time, demonstrating the count surviving across separate keypresses.

What’s actually happening

_G.TutorialPressCount or 0 reads as “whatever’s already stored in _G.TutorialPressCount, or 0 if there’s nothing there yet.” The very first press, nothing’s there yet (_G.TutorialPressCount is nil, which is falsy), so it becomes 0 + 1 = 1. Every press after that, the value really is sitting in _G from last time, so it becomes that value + 1. The or is doing all the work here — without it, _G.TutorialPressCount + 1 would error the very first time, since you can’t add 1 to nil.

This is the same idea Your First Menu uses for remembering whether a toggle is on or off — a whole table instead of one number, but the exact same _G.Something = _G.Something or {...} shape.

Try it yourself

• Add a second counter (_G.TutorialOtherCount) in the same script, incrementing independently — confirm both survive and update correctly together.
• Add a reset: put _G.TutorialPressCount = 0 at the top of the script, temporarily, run it once, then remove that line again. (This is a real technique — a one-time reset line you add, run, then delete.)
• Make it count down instead of up, starting from 10, and print "self-destructing in N" — stop it from going below 0 with an if check.
• Tutorial 8 reuses this exact _G pattern to count timer ticks instead of keypresses — see if you can predict what that code will look like before you get there.

Where this comes from

• Your First Menu: Three pieces, combined — the same pattern, immediately put to use in a real two-toggle menu.

Next: Tutorial 8: Making Time Pass on Its Own — everything so far has needed a keypress. Time to make something happen without you touching anything.