Which of the following statements about event handlers is true?

Event handlers are essential for responding to both user and system events. An event handler is a function that is executed when a specific event occurs, such as a user clicking a button or a system event like a browser loading an element. They allow developers to define how an application should respond to a wide variety of actions, which can be initiated by users (like mouse clicks or keyboard inputs) or automatically triggered by the system (such as loading events or timers).

The importance of event handlers lies in their ability to provide interactivity and dynamic behavior to applications, making them a core concept in event-driven programming. They are integral to the functionality of web applications, enabling developers to create responsive interfaces that react to different types of events as they happen.

Other statements do not accurately reflect the nature and functionality of event handlers. For example, while user interactions are a major source of events, event handlers also respond to various system-generated events, which means they are not limited to user interactions alone. Additionally, event handlers can be either synchronous or asynchronous, depending on their use case; thus, they are not required to be asynchronous. Finally, event handlers are typically attached to events when the application initializes, making them ready to respond immediately rather than being inactive until manually triggered