1. 构造函数
2. ExtendableEvent
3. 属性
4. bubbles
5. cancelable
6. composed
7. currentTarget
8. defaultPrevented
9. eventPhase
10. hashCode
11. isTrusted
12. matchingTarget
13. path
14. runtimeType
15. target
16. timeStamp
17. type
18. 方法
19. composedPath
20. noSuchMethod
21. preventDefault
22. stopImmediatePropagation
23. stopPropagation
24. toString
25. waitUntil
26. 运算符
27. 运算符 ==