Based on the other replies here it seems like it's to differentiate taps vs mouse clicks, keyboard events in js don't have a screenX or screenY property (you ca

Based on the other replies here it seems like it's to differentiate taps vs mouse clicks, keyboard events in js don't have a screenX or screenY property (you can run this in your browser console on this HN post to confirm): (() => { const logEvent = event => console.log({ coords: [event.screenX, event.screenY], type: event.type }); const input = document.querySelector("textarea"); // use "keydown" instead of "keypress" to detect all keyboard input instead of just character producing input input.addEventListener("keydown", logEvent); input.addEventListener("click", logEvent); })(); Type in or click on the reply text input and you'll see that the coords array is undefined for all keyboard events. I haven't tried this equivalent on a touch device however, so not sure how it's handled there.