The keydown event is fired when a key is pressed.

Unlike the keypress event, the keydown event is fired for all keys, regardless of whether they produce a character value.

The keydown and keyup events provide a code indicating which key is pressed, while keypress indicates which character was entered. For example, a lowercase "a" will be reported as 65 by keydown and keyup, but as 97 by keypress. An uppercase "A" is reported as 65 by all events.

This example logs the KeyboardEvent.code value whenever you press down a key.

<p>Focus the IFrame first (e.g. by clicking in it), then try pressing some keys.</p>
<p id="log"></p>

const log = document.getElementById('log');

document.addEventListener('keydown', logKey);

function logKey(e) {
  log.textContent += `${e.code}`;
}

An Input Method Editor (IME) is a program that enables users to enter characters that are not supported by their keyboard using some other key combination.

Since Firefox 65, the keydown and keyup events are now fired during IME composition (bug 354358). To ignore all keydown events that are part of composition, do something like this (229 is a special value set for a keyCode relating to an event that has been processed by an IME):

eventTarget.addEventListener("keydown", event => {
  if (event.isComposing || event.keyCode === 229) {
    return;
  }
  // do something
});

• keypress
• keyup
• Element: keydown event