Why do we need event bubbling and capturing?

Event bubbling is an event processing mechanism that is passed layer by layer from event source elements to the outside. Its significance is to simplify code, improve performance and implement event delegation. Event capture is an event processing mechanism opposite to event bubbling. Its significance is to preprocess events in advance, prevent event bubbling and implement custom event delegation. Event bubbling and capturing are two interdependent event processing mechanisms in js. Each has unique advantages and application scenarios. Through reasonable use, it can better organize and manage code, improve program performance and maintainability, and improve program performance and maintainability. Implement more flexible event handling.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

Event bubbling and capturing are two important concepts of the event processing mechanism in JavaScript. Their functions and meanings are as follows:

Event bubbling:

Event bubbling is An event processing mechanism that is passed layer by layer from event source elements to the outside. When an event occurs, the outermost element will first receive the event, and then pass it down layer by layer until it is passed to the event source element. This transmission method is like a bubble in water, starting from the outermost element and spreading outward layer by layer, so it is called "event bubbling".

The significance of event bubbling is:

(1) Simplify the code: Through event bubbling, we can bind the event handler to the outermost element without having to provide Child elements have individually bound handlers. When an event occurs, the event handler of the outermost element is automatically triggered, thus avoiding duplication of code.

(2) Improve performance: Since event bubbling is passed layer by layer, when processing events, only the event handler of the outermost element needs to be processed, instead of event handling for each child element. deal with. This improves the performance of the program to a certain extent.

(3) Implement event delegation: Through event bubbling, we can implement event delegation. Event delegation refers to binding the event handler to the parent element, and the parent element listens to the events of the child element. When an event occurs on a child element, the event handler of the parent element will be triggered, thereby realizing event processing on the child element. Event delegation can realize event processing of cross-level nested elements, improving the organization and maintainability of the code.

Event capture:

Event capture is an event processing mechanism opposite to event bubbling. When an event occurs, the event capture starts from the outermost element and is passed down to the target element layer by layer. This delivery method is like capturing, gradually deepening from the outside to the inside, so it is called "event capture".

The significance of event capture is:

(1) Preprocess events in advance: Through event capture, we can preprocess events on other elements before the target element handles the event. For example, you can obtain event context information and perform necessary verification and other operations during the capture phase to provide more information and preparation for subsequent target element event processing.

(2) Prevent event bubbling: In some cases, we may not want the event to continue to bubble up, but want to prevent its delivery during the capture phase. By calling the event.stopPropagation() method during the capture phase, you can prevent the event from continuing to pass upward, thereby avoiding unnecessary side effects on other elements.

(3) Implement custom event delegation: Like event bubbling, event capture can also be used to implement custom event delegation. By processing events in the capture phase, event delegation for cross-level nested elements can be achieved. This allows us to organize and handle events more flexibly.

To summarize, event bubbling and capturing are two interdependent event processing mechanisms in JavaScript. Each of them has unique advantages and application scenarios. By using them properly, we can better organize and manage code, improve program performance and maintainability, and achieve more flexible event handling. At the same time, it is also very important to choose which processing method to use based on specific needs.

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