Buttondown, a newsletter publisher, has a pretty standard CSS editor in its web app. You can edit the code and whenever you make any change, you can then press the Save button to make it go live:

The view also thoughtfully supports pressing ⌘S to do the same thing:

However, if there is nothing to save, ⌘S is ignored by the CSS editor, and falls back to the browser’s handling:

It feels logical: ⌘S only takes effect when the button is visible, otherwise why would a user press it? In a front-end sense, it might even seem thoughtful. We all witnessed web apps that greedily took over some interaction, and broke things in the process. Hell, I did that myself.

In theory, you – the user – take a careful look at the state of things, notice the button, and then press ⌘S.

But in practice? It’s none of the above. Fingers don’t look around. You might press ⌘S twice in a row. Or after an undo to an already saved state. Or after pressing another key so light it didn’t register. Or after just sitting down to an open document that’s already saved. Or because you weren’t sure if the previous ⌘S press worked. Or just to be sure. You might not know why, and you might not even notice. The beautiful raw power of ⌘S as a citizen of motor memory is that it’s automatic, mindless, habitual.

That’s why ⌘S here needs to be both deterministic and idempotent – if there is nothing to save, don’t let it fall back to the browser, don’t show an error message, don’t beep at the user. Just ignore the keystroke altogether.

It might feel funny, but there are tons of places in the UI that already look the other way. Off the top of my head:

• if you center align already center-aligned text in any writing app, the app just ignores you,
• if you press ⌘A to select all more than once, no one’s shouting at you,
• if you try to click a disabled button, the click gets quietly swallowed.

It gets a lot more interesting than these, but we’ll talk about more examples of “finger logic” in future posts.