1. 1. RxJS and Reactive Programming Ben Lesh Senior UI Engineer Netflix Edge Tools & Insights @benlesh
2. 2. Observables
3. 3. Observables TC39 proposal to add them to ES2016 (ES7) Angular 2 uses them and supports them in a first class way ReactJS will use them and support them in a first class way (Ask me about Ember after :P)
4. 4. Front End Development Mostly synchronous or asynchronous?
5. 5. We tend to think synchronously We write code in blocks that are read top to bottom, left to right. If this, then this, else this
6. 6. But What Are We Doing With Code? Handling User Input Animations AJAX/JSONP Web Sockets/SSE Updating DOM
7. 7. Most of these things are ASYNC! Handling User Input Animations AJAX/JSONP Web Sockets/SSE Updating DOM
8. 8. Async in JavaScript usually looks like this A function that gets called 0 to N times over time, generally being passed a value
9. 9. Asynchronous values Can be represented as collections!
10. 10. Collections today We have Iterables
11. 11. Iterable
12. 12. Observable is basically an Iterable turned inside-out
13. 13. RxJS Observables
14. 14. RxJS Observables (shorter)
15. 15. RxJS Observables (with error handling)
16. 16. In fact, this should look familiar
17. 17. But Observables handle more than one value, so we need to know when theyre done
18. 18. Observables Any number of values over any amount of time
19. 19. SO WHAT? We can represent values over time as a collection big deal.
20. 20. Set operations! Map Reduce Filter Concat Merge Zip FlatMap Take Skip
21. 21. Plus async set operations! Map Reduce Filter Concat Merge Zip FlatMap Take Skip Buffer Window CombineLatest Scan FlatMapLatest WithLatestFrom
22. 22. Confused Yet? Code Example!
23. 23. Observables for collections? I have arrays and iterables! Arrays already have map, filter, reduce
24. 24. Demo day at Netflix!
25. 25. We hooked it up to prod data and
26. 26. So what happened? Too much array map, filter, reduce!
27. 27. Array functional programming issues Iterating over arrays at each step Allocating new arrays at each step GCing those arrays
28. 28. Array filter, map, reduce
29. 29. RxJS Observables to the rescue! Stream Processing is nice
30. 30. Observable Stream Processing Data is only iterated over once No intermediary arrays created Less GC
31. 31. Observable filter, map, reduce
32. 32. Problem solved Less array allocation, less GC, less iterating over arrays
33. 33. RxJS Observables Are about to solve another problem
34. 34. Web Socket Connectivity Issues If you walked between buildings you lost the socket connection If you closed your lid for too long, you lost the socket connection If the network hiccupped or went down, you lost the socket connection If the server has an issue or restarts, you lose the socket connection If youre using 4G and your singal gets too low, you lose the socket connection
35. 35. Basically you had to stay very, very still..
36. 36. Multiplexing Web Sockets Connect to the socket Send a subscription message for each data stream you care about Group the incoming messages by data stream Send an unsubscribe message when youre done with a stream If all streams are disconnected, close the socket.
37. 37. Reconnecting Multiplexed Web Sockets Is A Pain Reconnect the socket Resend all subscriptions for previously subscribed streams If youre offline, wait for an online event, and reconnect Add a delay and retry again (exponential) What if the user switches views and needs different data streams during this?
38. 38. Observables Are Lazy Execute code upon subscription to set up the underlying data stream Execute code upon disposal to teardown the underlying data stream
39. 39. So you can do things like Setup a web socket on subscription Close the web socket on disposal Send an AJAX request Abort the AJAX request on disposal Setup an event listener Automatically remove event listeners on disposal
40. 40. This is nice Setup a web socket on subscription Close the web socket on disposal
41. 41. Observables can be retried or repeated Simply by subscribing more than once!
42. 42. Even better! RxJS has operators: retry, retryWhen and repeat
43. 43. Code Example
44. 44. Application Development Is about data flow
45. 45. How does your data flow through your app? What events cause variables to be produced How are those variables used and for what? Are you sure youre containing side-effects?
46. 46. RxJS makes this easier to reason about (with practice)
47. 47. Thinking in streams Imagine every variable (not consts) is a stream To get it, you need to figure out where it comes from It could come from other variables, or it could come from an event Figure out your side effects, these are the exit points for your data flow
48. 48. Thinking in streams var c = a + b; // do something with c
49. 49. Thinking in streams var cStream = Observable.combineLatest(aStream, bStream, (a, b) => a + b); cStream.subscribe(c => { // do something with c });
50. 50. Data Flow Entry and Exit Common entry points User input Network I/O Properties set Events handled Common exit points State Persistence View Renders Emitting events
51. 51. RxJS entry and exit observable sources for entries do() and subscribe() for exits
52. 52. The idea is to keep your data flow contained And control those side effects
53. 53. Recap Any number of values, any amount of time Are lazy, dont do anything until you subscribe Embody the set up and tear down of their underlying data sources Can retry/repeat Use do() and subscribe() for side-effects Observables were designed from the beginning to be cancellable
54. 54. Resources RxJS 2 on GitHub: https://github.com/Reactive-Extensions/RxJS Talk Examples: https://github.com/blesh/rx-talk-may-2015 RxSocketSubject: https://github.com/blesh/RxSocketSubject RxJS 3 (coming soon): https://github.com/ReactiveX/RxJS Observable Spec: https://github.com/jhusain/observable-spec Async Generator Proposal: https://github.com/jhusain/asyncgenerator
55. 55. Who to follow @headinthebox Erik Meijer (Rx) @jhusain Jafar Husain (TC39 Observable) @mattpodwysocki Matt Podwysocki (RxJS) @jeffbcross Jeff Cross (Angular) @victorsavkin Victor Savkin (Angular) @benlesh (me) @benjchristensen Ben Christensen (RxJava)
56. 56. Questions? Comments? Corrections? @benlesh blesh@netflix.com ben@benlesh.com http://github.com/blesh