关于DOM 事件流的三个阶段_html/css_WEB-ITnose
一丶 流
什么是流?
比如 react 中的单项数据流,Node.js 中的流,或者本文中的 DOM 事件流,都是流的具体体现。专业地讲,流是程序输入或输出的一个连续的字节序列;通俗地讲,流是有方向的数据。
二丶 事件流
什么是事件流?
假想一下,现在有一组同心圆,你把手指在最里面的圆心上,与此同时,你也正在指着外层的其他同心圆。假设最里面的圆是 DOM 中的一个按钮,那就是说,你点击按钮这个元素的同时,也点击了他的所有父级元素。那么这个点击事件 DOM 要怎么处理呢?事实上,这个点击事件并非只是简单地在被点击的元素上发生一次。那么点击事件是谁先得到通知并响应呢?
事件捕获
事件捕获就是指被点击元素的父级元素应该先接收到事件,并向下传播,就像例子中的按钮点击事件,接收到事件的元素顺序应该为 window > document > body > button.
事件冒泡
事件冒泡跟事件捕获好顺序相反,认为应该是被点击的具体元素先接受到事件:button > body > document > window.
事件阶段
当一个 DOM 事件发生时,要经历三个阶段:
1. 从文档的根节点流向目标对象 ---> 捕获阶段;
2. 在目标对象上被触发 ---> 目标阶段;
3. 回溯到文档的根节点 ---> 冒泡阶段。
三丶 卵用
通过事件监听(addEventListener(type,callback,true))在父级元素捕获事件,可以阻止事件冒泡(stopPropergation())引起的问题。

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