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