Blogging Task 5
Document Object Model (DOM).

example of DOM tree

This model is now compatible with most web browsers. It provides a standard set of objects that can be used in web programming, making it easier to access and change web documents. The Document Object Model looks at documents as a tree. Each of the elements within the document is regarded as a branch on a tree, and these elements can be accessed and modified through the DOM. Also, it is platform and language independent.

1. Without modifying what was programmed earlier, new commands can be typed out to make the desired modification to the web page.

The difference between keydown and keypress

2.There is a difference between a “character” and a “key”. A “key” is a physical button on the computer’s keyboard while a “character” is a symbol typed by pressing a button. In theory, the keydown and keyup events represent keys being pressed or released, while the keypress event represents a character being typed. The implementation of the theory is not same in all browsers

EVENT Bubbling

3. Events which are designated as bubbling will initially proceed with the same event flow as non-bubbling events. The event is dispatched to its target EventTarget and any event listeners found there are triggered. Bubbling events will then trigger any additional event listeners found by following the EventTarget’s parent chain upward, checking for any event listeners registered on each successive EventTarget. This upward propagation will continue up to and including the Document. EventListeners registered as capturers will not be triggered during this phase. The chain of EventTargets from the event target to the top of the tree is determined before the initial dispatch of the event. If modifications occur to the tree during event processing, event flow will proceed based on the initial state of the tree.

Any event handler may choose to prevent further event propagation by calling the stopPropagation method of the Event interface. If any EventListener calls this method, all additional EventListeners on the current EventTarget will be triggered but bubbling will cease at that level. Only one call to stopPropagation is required to prevent further bubbling.

Canceling of the event

4.Some events are specified as cancelable. For these events, the DOM implementation generally has a default action associated with the event. An example of this is a hyperlink in a web browser. When the user clicks on the hyperlink the default action is generally to active that hyperlink. Before processing these events, the implementation must check for event listeners registered to receive the event and dispatch the event to those listeners. These listeners then have the option of canceling the implementation’s default action or allowing the default action to proceed. In the case of the hyperlink in the browser, canceling the action would have the result of not activating the hyperlink.

Cancelation is accomplished by calling the Event’s preventDefault method. If one or more EventListeners call preventDefault during any phase of event flow the default action will be canceled.

Different implementations will specify their own default actions, if any, associated with each event. The DOM does not attempt to specify these actions.


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