defaultPrevented

defaultPrevented is a boolean property of the Event interface in web browsers. It indicates whether preventDefault() has been called on a given event. When true, the event’s default action should be prevented; when false, the default action may proceed.

Whether defaultPrevented can be set depends on the event’s cancelable flag. If an event.cancelable is true, calling preventDefault() on that event sets defaultPrevented to true. If the event is not cancelable, calling preventDefault() has no effect and defaultPrevented remains false. The value is useful for coordinating between multiple event handlers and the user agent’s own default actions.

During event dispatch, the default action associated with a cancelable event will be suppressed when defaultPrevented is true. Examples include following a link, submitting a form, or triggering a browser’s default behavior for certain key presses. In handlers, code may check event.defaultPrevented to determine whether a previous handler or the user agent prevented the default action, and adapt behavior accordingly.

Usage commonly involves calling preventDefault() within an event handler to stop a default action, such as preventing a form from submitting so that custom validation can run first. Later logic can inspect event.defaultPrevented to decide how to proceed. Some older environments used alternative mechanisms, such as setting returnValue to false, to achieve a similar effect.

See also: Event.preventDefault(), Event.cancelable, Event.