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Episode 4 of 16 · Web development, end to end

Async JavaScript: the event loop, promises, and the order things really run

Chapters

1. One lane only0:00
2. Frames on a pile0:14
3. Blocking, literally0:29
4. The host does the waiting0:45
5. The task queue1:00
6. The loop itself1:18
7. A note left with a stranger1:34
8. The shape everyone shows1:48
9. Error first, every level2:06
10. Inversion of control2:22
11. Try catch cannot reach2:38
12. What was actually missing2:53
13. A cloakroom ticket3:09
14. Three states, one move3:23
15. Then, catch, finally3:41
16. The chaining contract3:56
17. Errors fall to the catch4:13
18. Two ways a chain breaks4:30
19. A second, shorter line4:48
20. The rule, exactly5:06
21. The famous puzzle5:24
22. Zero is not zero5:43
23. Starving the loop6:01
24. Where microtasks come from6:21
25. A bookmark6:41
26. The same machine6:57
27. Try catch is real again7:14
28. Suspend, not block7:32
29. The sequential await trap7:49
30. Two await traps8:09
31. One trip, four letters8:26
32. All fails fast and leaves8:42
33. AllSettled reports9:01
34. Race, and timeouts9:18
35. Any takes a winner9:37
36. Cancellation, awkwardly9:56
37. One machine10:14

Async JavaScript: the event loop, promises, and the order things really run. Open any web page and everything you write runs on a single thread. One thing at a time, in order, with no help. And yet a page can wait on the network, animate, and answer a click

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