Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Availability

Methods

handleEvent( )

In languages such as Java that do not allow functions to be passed as
arguments to other functions, you define an event listener by
defining a class that implements this interface and includes an
implementation for this handleEvent( ) method.
When an event occurs, the system calls this method and passes in an
Event object that describes the event.

In JavaScript, however, you define an event handler simply by writing
a function that accepts an Event object as its argument. The name of
the function does not matter, and the function itself is used in
place of an EventListener object. See the Section
section.

Description

This interface defines the structure of an event listener or event
handler. In languages such as Java, an event listener is an object
that defines a method named handleEvent( ) that
takes an Event object as its sole argument. In JavaScript, however,
any function that expects a single Event argument, or a function that
expects no argument, can serve as an event listener.

Example

// This function is an event listener for a "submit" event
function submitHandler(e) {
// Call a form-validation function defined elsewhere
if (!validate(e.target))
e.preventDefault(  );  // If validation fails, don't submit form
}
// We might register the event listener above like this
document.forms[0].addEventListener("submit", submitHandler, false);

See Also

Event, EventTarget; Chapter 19

Passed to

EventTarget.addEventListener( ), EventTarget.removeEventListener( )