Altkey

altKey is a boolean property of the KeyboardEvent interface used in web development. It indicates whether the Alt modifier key was pressed at the time the event occurred. The value is true when either the left or right Alt key is held down during the event, such as during a keyboard shortcut that combines Alt with another key. On some keyboard layouts, the AltGr key (often the right Alt) may interact with Alt in various ways, so behavior can vary slightly across environments.

Common usage involves checking the property in event handlers for keydown, keyup, or keypress events. This allows developers to implement custom shortcuts or to alter behavior when Alt is used. A typical pattern is to combine altKey with the event’s key or code to determine the exact action. For example:

window.addEventListener('keydown', function(e) {

if (e.altKey && (e.key.toLowerCase() === 's')) {

e.preventDefault();

saveDocument();

}

});

Compatibility and considerations: altKey is widely supported in modern browsers and across major operating systems. However, Alt-related shortcuts can conflict with built-in browser or OS shortcuts, so developers often call preventDefault to avoid unexpected navigation or menu activation. When designing shortcuts, it’s also common to pair altKey with other modifiers (ctrlKey, shiftKey, metaKey) to create distinct, accessible combinations.

See also: ctrlKey, shiftKey, metaKey, KeyboardEvent, key, code.