keyDown

The keydown event is fired when a key is pressed down on the keyboard. It is part of the KeyboardEvent interface and can be listened for on window, document, or individual elements using addEventListener or the onkeydown handler. The event fires for all keys, including non‑printing keys such as Escape, Arrow keys, and function keys.

In the standard event sequence, keydown occurs before keypress (which is primarily for printable characters and is deprecated in modern web practice) and before keyup. For most keys you will see a keydown, then a keyup when the key is released; printable characters may also generate a keypress event on some platforms, though this is being phased out in favor of keydown/keyup.

The event object carries several useful properties. key is the value of the key pressed, reflecting the current layout and modifiers (for example, "a" or "A" depending on Shift). code identifies the physical key on the keyboard (for example, "KeyA" or "ArrowLeft"), which is layout‑independent. keyCode, which is deprecated, and which are legacy ways to identify keys. Other properties include altKey, ctrlKey, shiftKey, and metaKey to detect modifier keys; repeat indicates the key is being held down; isComposing indicates an IME composition is in progress. Methods such as preventDefault() can stop the browser’s default action for that key, and stopPropagation() can prevent the event from bubbling up the DOM chain.

Keydown listeners are commonly used for keyboard shortcuts, game controls, or live input handling. They bubble by default, though capture can be used if needed. Because behaviors can vary with keyboard layout and browser, prefer e.key and e.code over deprecated codes and test across target environments.