Alternative for event's deprecated KeyboardEvent.which property

MDN states that KeyboardEvent.which is deprecated. How can I substitute it for a non-deprecated version?

For example, I have the following:

window.onkeydown = (event) => { console.log(event.which); }

I thought event.key.charCodeAt() could substitute event.which, but this won't work for keys such as ALT, CTRL or ENTER, and it only works if event.key.length === 1:

window.onkeydown = (event) => { console.log(event.key.charCodeAt()); }

To recap, event.which != event.code and event.which != event.key, therefore I am unable to simply use event.key.

Is there a substitute for event.which which detects combination keypresses including ALT, CTRL or ENTER?

from Alternative for event's deprecated KeyboardEvent.which property