Event Bubbling vs. Capturing: How Does Event Propagation Work in the DOM?

Understanding Event Bubbling and Capturing

In HTML DOM events, when an element within another element triggers an event, the event can propagate through the hierarchy of elements. Depending on the event propagation mode selected, the order in which elements receive the event changes.

Event Bubbling

With event bubbling, the event is first captured and handled by the innermost element, traveling "up" through the DOM hierarchy. As a result, the event target element handles the event first, followed by its parent, and so on.

Event Capturing

In contrast, with event capturing, the event is first captured by the outermost element and propagates "down" through the hierarchy. Thus, the root element handles the event before its child elements.

Choosing Bubbling vs. Capturing

The choice of event bubbling or capturing depends on the desired event handling behavior.

• Use bubbling when the event should be handled by multiple elements and the order of handling is unimportant. It is also useful for delegating event handling to a parent element.
• Use capturing when it is necessary to intervene before the event reaches the target element. This is often used to prevent default behavior or to handle events consistently across different element types.

Example

In the HTML structure:

<div>

If a click event occurs on the

element, the following occurs:

• Bubbling: li -> ul -> div
• Capturing: div -> ul -> li

Note:

• Event capturing was once supported only by Netscape, while bubbling was preferred by Microsoft. Today, both are standardized by the W3C.
• Event bubbling may have a slight performance overhead compared to capturing for complex DOM structures.
• Event handlers can be registered for either bubbling or capturing using the addEventListener method with the optional useCapture parameter.

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