冒泡和捕获
捕获
element1的事件首先被触发，其次element2的事件被触发
| |
---------------| |-----------------
| element1 | | |
| -----------| |----------- |
| |element2 \ / | |
| ------------------------- |
| Event CAPTURING |
-----------------------------------
冒泡
element2首先被触发，其次element1被触发
/ \
---------------| |-----------------
| element1 | | |
| -----------| |----------- |
| |element2 | | | |
| ------------------------- |
| Event BUBBLING |
-----------------------------------
W3C event model
W3C has very sensibly decided to take a middle position in this struggle. Any event taking place in the W3C event model is first captured until it reaches the target element and then bubbles up again. 首先被捕获，直到到达目标元素，然后再被冒泡出去**
| | / \
-----------------| |--| |-----------------
| element1 | | | | |
| -------------| |--| |----------- |
| |element2 \ / | | | |
| -------------------------------- |
| W3C event model |
------------------------------------------
You, the web developer, can choose whether to register an event handler in the capturing or in the bubbling phase. This is done through the addEventListener() method explained on the Advanced models page. If its last argument is true the event handler is set for the capturing phase, if it is false the event handler is set for the bubbling phase.
开发者可以自己选择是在捕获还是冒泡阶段来注册事件，如果addEventListener的最后一个参数是true，那么就是在捕获阶段注册；如果是false，是在冒泡阶段注册。
Suppose you do
element1.addEventListener('click',doSomething2,true)
element2.addEventListener('click',doSomething,false)