JavaScript/Notes/IBD

Interface Based Design

Using a common interface, different Event registries handle different types of event registration:

1. Event handler properties. Browser agnostic.
2. Dom Event callback registration methods, considering delegation, IE event model, browser anomalies.

Source: https://github.com/GarrettS/EventPublisher

The implementation can be swapped out as needed for any given scenario or context, without having to try to accommodate every conceivable situation in one monolithic class.

DOM Events

DOM events need an adapter for addressing the great difference in old IE's event model, with attachEvent, getting a event properties such as target, and, relatedTarget, and addressing delegate listeners (See: DOM Event Flow).

Custom Events

Custom Events are user defined so do not need any adapter. Custom do not need "on" conditionally prefixed to the event name, however DOM Event handler properties do, e.g. <source lang="javascript"> EventPublisher.get(document, "onclick"); </source>

The custom registry does not try to normalize the event, either. This can be a problem when this registry is used for DOM 0 Event handlers.

In that situation, the client can access the static adapter methods DomEventPublisher.getTarget(ev) and DomEventPublisher.getRelatedTarget(ev).

Encapsulate the Parts that Vary

Event handler properties are useful for custom events and DOM events.

For DOM compatibility, it is often necessary to have methods that will handle old IE event model or work with delegate listeners (See: DOM Event Flow).

Common Interface

Each interface shares the following methods: <source lang="javascript"> // Static: get(src, sEvent); // Gets an event publisher. addCallback(src, sEvent, callback); removeCallback(o, type, cb); // useCapture for DOM.

// Instance: eventPublisher.addCallback(sEvent, callback); eventPublisher.removeCallback(sEvent, callback); </source>

The DOM events interface has an additional parameter, `useCapture` for the capturing phase of the Event phase in removeCallback, used internally.

Event Handler Properties

Each event is a property name. The value is a function or null. The pattern works equally well for custom events on user-defined objects and DOM events.

DOM Elements <source lang="javascript"> el["onclick"] = function(ev) {

 alert(this);

};</source>

Custom Objects and Events <source lang="javascript"> userPicker.onuserselected = function(ev) {

 console.log(ev.user + " chosen.");

}; </source>

Event Listener Interface

<source lang="javascript"> el.addEventListener("click", function(ev) {

 alert("clicked");

}, false); </source>

Custom objects <source lang="javascript"> userPicker.addCallback("onuserselected", function(ev) {

 console.log(ev.user + " chosen.");

}); </source>