Syncing Async

I bet you think “callback hell” is about function nesting and levels of indentation. Not so much. I bet you’ve heard that Promises replace callbacks. Nope.

We need some clarity on what async flow control is all about in JavaScript. We’ll explore the perils of “Inversion of Control”, and see just what hell that leads us to. Then we’ll talk about promises as “continuation events” for function calls, and abstractions on top of promises that clean up our code. Finally, we’ll see how generators give us synchronous-looking async, and even how we can create cooperative concurrency with coroutines.

Yield those confused async notions and control your flow. I promise we’ll get your thoughts in order.

Transcript

1. syncing async kyle simpson @getify http://getify.me
2. vs. parallel async
3. threads
8. event-loop concurrency
9. 1 2 3 4 1 2 3
10. 1 2 3 4 1 2 3 done! done!
11. async patterns
12. callbacks == continuations
13. callbacks got problems 2 major ^
14. “callback hell”
15. still “callback hell”
16. inversion of control
18. trust: 1. not too early 2. not too late 3. not too many times 4. not too few times 5. no lost context 6. no swallowed errors ...
20. nested callbacks are not reasonable
23. we write
24. we think
25. js thinks
26. sync-looking async synchronous sequential blocking
27. hell is callbacks -Sartre
28. promise: future value
29. promise: “completion” event
32. promises: 1. only resolved once 2. either success OR error 3. messages passed/kept 4. exceptions become errors 5. immutable once resolved
33. uninversion of control
34. steps
35. promise: flow control
37. scenario: load files in parallel, render in order, but ASAP
39. cool story, bro. but...
41. scenario: timeout of a promise
43. blog.getify.com/promises-part-1/ github.com/getify/native-promise-only
44. promise abstractions
45. sequence = series of automatically chained promises
46. github.com/getify/asynquence async + sequence = asynquence
48. remember? load files in parallel, render in order, but ASAP
51. promises without all the fuss
52. gimme moar sync
53. ES6 generators davidwalsh.name/es6-generators
54. generator + promises yield promises
55. ES2016 async ? github.com/lukehoban/ecmascript-asyncawait
58. github.com/getify/a-tale-of-three-lists
59. “if you like it then you shoulda put async in it...”
60. thx! kyle simpson @getify http://getify.me