Keyboard Event Viewer (event.key / event.code / keyCode)

event.key reflects the character the key produces given the current layout and modifiers (e.g. "a" or "A" or "?" depending on Shift), while event.code identifies the physical key on the keyboard regardless of layout or language (e.g. "KeyA" always means the key labeled A on a US QWERTY layout, even if the active layout remaps it). Use event.code for layout-independent shortcuts (like WASD game controls) and event.key when you care about the actual character typed.

Yes, event.keyCode is deprecated in the DOM spec in favor of event.key and event.code, and its numeric values were never fully standardized across browsers/OSes for punctuation and non-US layouts. It still works everywhere for backward compatibility, but new code should prefer event.key/event.code.

Modifier keys (Shift, Ctrl, Alt, Meta) fire their own keydown events with their own key/code/keyCode (e.g. Shift is key: "Shift", code: "ShiftLeft" or "ShiftRight", keyCode 16) separately from the letter key event that follows while held.

location distinguishes keys that appear more than once on a keyboard: 0 = standard, 1 = left-side (e.g. left Shift/Ctrl/Alt), 2 = right-side, and 3 = the numeric keypad (e.g. Numpad1 vs the top-row Digit1).

No. The key listener runs entirely in your browser with a standard keydown event listener — nothing is uploaded or logged to a server.