KeyUp

In web development, keyup is a keyboard event that fires when the user releases a key after pressing it. It is a type of DOM event that can bubble up through the document tree and is typically listened for on elements with keyboard focus, such as input and textarea, or on the document.

Keyup follows keydown (and usually keypress, though keypress is deprecated) and represents the moment the key is released. It fires for most keys, including letters, digits, and control keys like Enter or Escape. If multiple keys are pressed at once, each key's release will trigger its own keyup event when released.

The event handler receives a KeyboardEvent object. Useful properties include key, which contains the character or action (for example 'a' or 'Enter'), and code, which identifies the physical key (for example 'KeyA' or 'Enter'). Modern code generally avoids deprecated keyCode and which properties in favor of key and code. The event also exposes modifier flags such as altKey, ctrlKey, shiftKey, and metaKey, and a boolean repeat that indicates auto-repeated keydowns.

Common uses include performing validation or finalizing input after the user finishes typing, or implementing lightweight search suggestions. Because keyup occurs after the input value often changes, it is sometimes used in tandem with the input event to avoid reacting to every keystroke.

Cross-browser notes: modern browsers implement keyup consistently as part of the KeyboardEvent interface. For compatibility, prefer e.key and e.code and fall back to e.keyCode only if necessary. Attach listeners with addEventListener('keyup', handler) on the appropriate element or window.