Event bubbling: Master the event delivery rules in the browser

Event bubbling: Master the event delivery rules in browsers

Event bubbling refers to when an event occurs on an element in a web browser , its parent element will also trigger the same event in turn. Understanding and mastering the rules of event bubbling is very important for web developers, as it can help us optimize code and improve event processing efficiency. This article will introduce the basic principles of event bubbling and the rules of event delivery in browsers.

The principle of event bubbling

Before understanding event bubbling, we need to understand the hierarchical structure of events. In an HTML document, all elements can be seen as nested within other elements, forming a hierarchical structure with a parent-child relationship. When an event occurs on an element, the event is passed to its parent element, and then to higher-level ancestor elements, until it is passed to the root element of the HTML document. This delivery process is called event delivery, and the delivery process from child elements to parent elements is called event bubbling.

Through event bubbling, we can achieve the effect of an event being monitored and processed by multiple elements at the same time. For example, when we click a button, the click event on the button element will bubble to its parent element, and then to the higher-level ancestor element. We can add corresponding event listeners on parent elements or ancestor elements to capture and handle bubbling events.

Event delivery rules in browsers

In browsers, event bubbling is the default event delivery method. This means that when an event occurs on an element, it will be passed to the parent element of the element, and then to the ancestor element higher up.

Specifically, event delivery in browsers follows the following rules:

1. Events are delivered starting from the triggered element, and then propagated up the DOM tree until they reach the root element.
2. By default, during event delivery, the execution order of event processing functions is from inside to outside. That is, the event processing function on the child element is executed first, and then the event processing function on the parent element is executed until the root element.
3. We can prevent the event from continuing to be delivered by preventing the event from bubbling. In the event handling function, use the event.stopPropagation() method to prevent the event from continuing to bubble.
4. During the event delivery process, the element that the event was initially triggered can be obtained through the event.target attribute. Because events may pass through multiple elements during delivery, event.target can help us locate the source element that actually triggered the event.

Summary

Event bubbling is a rule for event delivery in browsers. Through it, we can achieve the effect of multiple elements listening and processing an event at the same time. It is very important for web developers to understand and master the principle of event bubbling and the event delivery rules in browsers.

In actual development, we can use event bubbling to optimize code, reduce the number of event monitoring and processing, and improve page performance. At the same time, we can also control the delivery of events by preventing event bubbling to ensure that events are only processed on the elements we want.

Through in-depth research and practical application, we can better master the event bubbling rules in the browser, improve development efficiency, and provide users with a better interactive experience.

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