en.javascript.info/2-ui/3-event-details/5-keyboard-events/2-check-sync-keydown/solution.md

We should use two handlers: document.onkeydown and document.onkeyup.

Let's create a set pressed = new Set() to keep currently pressed keys.

The first handler adds to it, while the second one removes from it. Every time on keydown we check if we have enough keys pressed, and run the function if it is so.