Capture first or bubble first? Analyze the advantages and disadvantages of event processes

Catch first or bubble first? Analyzing the advantages and disadvantages of event process

Event process is an important concept in web development. It describes the process of events from occurrence to processing. There are two main process models when handling events: capture then bubble and bubble then capture. These two models have their own advantages and disadvantages in different scenarios, and you need to choose the appropriate model based on the actual situation.

Capture first and then bubble means that the event capture phase is executed before the event bubbling phase. The event capture phase starts at the root node of the event target and proceeds downward until it reaches the target element. Then, during the event bubbling phase, the event starts from the target element and is passed upwards along the superior elements of the DOM tree.

On the contrary, the event capture phase is executed after the event bubbling phase. The event bubbling phase starts from the event target element and passes upward along the superior elements of the DOM tree. Then, in the event capture phase, the event starts from the root node of the target element and is passed down level by level until it reaches the target element.

So, what are the advantages and disadvantages of the two models: capture first and then bubble and first bubble and then capture?

The advantage of the capture first and then bubble model is that the event capture phase can capture events and preprocess them. This means we can intercept and modify events before they reach the target element. This is useful in certain scenarios, such as in a form where we can validate and filter data before the user enters it. In addition, since events are passed down from the root node, the triggering order of event processing functions is consistent with the nesting level of elements, which makes event processing more intuitive.

However, the capture first and then bubble model also has some disadvantages. First of all, the capture phase can interrupt event delivery. If a handler function calls the event.stopImmediatePropagation() method in the capture phase, the bubbling phase will not be executed, which may lead to some unexpected situations. Secondly, since the event is triggered twice at the target element, once in the capture phase and once in the bubbling phase, performance issues may occur, especially for some complex event handling functions.

The advantage of the bubble first and then capture model is that the event processing function will only be called once, which can reduce some unnecessary performance consumption. In addition, because the event bubbling phase is consistent with the nesting level of the element, the execution order of the processing functions is more intuitive.

However, the bubble first and capture later model also has some disadvantages. First of all, since the event cannot be intercepted and modified during the event bubbling stage, the event cannot be preprocessed before the target element. Second, the order in which the processing functions are fired may not be consistent with the hierarchy of elements, which may lead to some unexpected results.

To sum up, the two event process models of capturing first and then bubbling and first bubbling and then capturing each have their own advantages and disadvantages. In actual development, we should choose the appropriate model based on actual needs. If the event needs to be preprocessed or the execution order of the processing functions is consistent with the hierarchy of the elements, then the capture first and then bubble model may be more suitable; if you want to reduce performance consumption or the firing order of the processing functions is consistent with the hierarchy of the elements, then A bubble first then capture model may be more suitable. Ultimately, a reasonable choice of event process model will help improve the performance and user experience of web applications.

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