Scratching the Surface of RxJS

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@KevinSalter

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ReactiveX

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just scratching the surface of ReactiveX and RxJS

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`whoami` Front-End Developer | 7Geese @KevinSalter Kevin Salter

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road map 1. What is ReactiveX and RxJS? 2. Why would I want to learn and use it? 3. How does it work? key points

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TIL r/mildlyinteresting/

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So, what is ReactiveX?

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ReactiveX is a library for composing asynchronous and event-based programs by using observable sequences.

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ReactiveX is a library for composing asynchronous and event-based programs by using observable sequences. • RxJava • RxJS • Rx.PY • RxClojure • RxSwift • and more… • RxScala • Rx.rb • rx.NET Different flavours:

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Reactive-Extensions/RxJS v 2.1.0 - 4.0 RxJS • invented at Microsoft around 2009 • open sourced in November of 2012 the early years…

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ReactiveX/rxjs v 5.0.0-beta.12 RxJS 5.0 is internally simpler, (4.3x average) faster, and designed to be aligned with the TC39 proposal for Observables as of Sept. 9th, 2016

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RxJS v 5.0.0-beta.12

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RxJS Contributors

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What is Reactive Programming?

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FRP

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Functional Reactive Programming

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Functional programming typically involves declaratively composing functions to process data and return a result while avoiding things like changing states and mutable data.

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Reactive programming is programming with asynchronous data streams.

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A data stream is a collection of data over time

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You can also think of data streams as a never-ending array

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static array vs stream https://jsbin.com/telofe/29/edit?js,console

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Observables can model both synchronous and asynchronous data

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Marble Diagrams

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Anatomy of a Marble Diagram

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Anatomy of a Marble Diagram

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Anatomy of a Marble Diagram

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Anatomy of a Marble Diagram

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http:/ /rxmarbles.com

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1. not mutating any data, just returning new streams 2. no need to maintain state, i.e. a counter, or building up an array 3. also, notice there are no control ﬂow statements (i.e. if, else) 4. no need to set/clear setTimeouts or setIntervals 5. specify the dynamic behaviour of a value completely at the time of declaration 6. (ideally) more terse, cleaner, more maintainable code What’s the advantage over event listeners, or an imperative programming style, for example?

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what is RxJS?

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“RxJs is LoDash or Underscore for async”

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Terms • Observable (Core Type) • Observer, Schedulers, Subjects (Satellite Types) • Operators (inspired by Array#extras, i.e. map, filter, reduce)

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Rx.Observable

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code examples https://jsbin.com/xamobok/60/edit?js,console

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Observables are lazy Push collections of multiple values.

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speaking of promises…

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• DOM events • Animations • AJAX • WebSockets • Server Sent Events (SSE) • Alternative inputs (voice, joystick, etc.) Types of async in modern web applications

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• DOM events (0-n values) • Animations (cancellable) • AJAX (1 value) • WebSockets (0-n values) • SSE (0-n values) • Alternative inputs (0-n values) Promises only really make sense for one of these

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Observables come in 2 temperatures

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Hot Cold

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Cold Observables are “cold” by default. “Cold” observables create a new producer each time a consumer subscribes to them.

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Hot Hot observables share a single producer with every consumer that subscribes to them. Hot observables are "live" sequences, meaning that they are happening whether we observe them or not.

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Cold Observables are like recorded video Hot Observables are like live video

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cold / hot example https://jsbin.com/seduni/16/edit?js,console

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more about operators…

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“RxJs is like LoDash for asynchronous data streams”

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methods that perform calculations on values Operators

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Types of Operators • Transformation map, scan, switchMap, • Combination combineLatest, concat, merge, startWith • Creation from, fromPromise, of • Filtering debounceTime, distinctUntilChanged, take, takeUntil • Multicasting share, publish • Error Handling catch, retry, retryWhen • Utility do, let, delay

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Aggregate All Amb and_ And Any apply as_blocking AsObservable AssertEqual asyncAction asyncFunc Average averageDouble averageFloat averageInteger averageLong blocking Buffer bufferWithCount bufferWithTime bufferWithTimeOrCount byLine cache case Cast Catch catchException collect collect CombineLatest combineLatestWith Concat concat_all concatMap concatMapObserver concatAll concatWith CombineLatest combineLatestWith Concat concat_all concatMap concatMapObserver concatAll concatWith Connect connect_forever cons Contains controlled Count countLong Create cycle Debounce decode DefaultIfEmpty Defer deferFuture Delay delaySubscription delayWithSelector Dematerialize Distinct DistinctUntilChanged Do doAction doOnCompleted doOnEach doOnError doOnRequest doOnSubscribe doOnTerminate doOnUnsubscribe doseq doWhile drop dropRight dropUntil dropWhile ElementAt ElementAtOrDefault Empty empty? encode ensures error every exclusive exists expand failWith Filter filterNot

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Finally finallyAction finallyDo find findIndex First FirstOrDefault firstOrElse FlatMap flatMapFirst flatMapIterable flatMapIterableWith flatMapLatest flatMapObserver flatMapWith flatMapWithMaxConcurrent flat_map_with_index flatten flattenDelayError foldl foldLeft for forall ForEach forEachFuture forIn forkJoin From fromAction fromArray FromAsyncPattern fromCallable fromCallback FromEvent FromEventPattern fromFunc0 from_future from_iterable from_list fromNodeCallback fromPromise fromRunnable Generate generateWithAbsoluteTime generateWithRelativeTime generator GetEnumerator getIterator GroupBy GroupByUntil GroupJoin head headOption headOrElse if ifThen IgnoreElements indexOf interleave interpose Interval into isEmpty items Join join (string) jortSort jortSortUntil Just keep keep-indexed Last lastOption LastOrDefault lastOrElse Latest Latest length let letBind limit LongCount ManySelect Map MapCat map-indexed map_with_index Materialize Max MaxBy Merge mergeAll merge_concurre mergeDelayErro mergeObservab

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mergeWith Min MinBy MostRecent Multicast nest Never Next none nonEmpty nth ObserveOn ObserveOnDispatcher observeSingleOn of of_array ofArrayChanges of_enumerable of_enumerator ofObjectChanges OfType ofWithScheduler onBackpressureBlock onBackpressureBuffer onBackpressureDrop OnErrorResumeNext onErrorReturn onExceptionResumeNext orElse pairs pairwise partition partition-all pausable pausableBuffered pluck product Publish PublishLast publish_synchronized publishValue raise_error Range Reduce reductions RefCount Repeat repeat_infinitely repeatWhen Replay rescue_error rest Retry retry_infinitely retryWhen Return returnElement returnValue runAsync Sample Scan scope Select (alternate name of Map) select (alternate name of Filter) selectConcat selectConcatObserver SelectMany selectManyObserver select_switch selectSwitch selectSwitchFirst selectWithMaxConcurrent select_with_index seq SequenceEqual sequence_eql?

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SequenceEqualWith Serialize share shareReplay shareValue Single SingleOrDefault singleOption singleOrElse size Skip SkipLast skipLastWithTime SkipUntil skipUntilWithTime SkipWhile skip_while_with_index skip_with_time slice sliding slidingBuffer some sort sort-by sorted-list-by split split-with Start startAsync startFuture StartWith stringConcat stopAndWait subscribe SubscribeOn SubscribeOnDispatcher subscribeOnCompleted subscribeOnError subscribeOnNext Sum sumDouble sumFloat sumInteger sumLong Switch switchCase switchIfEmpty switchLatest switchMap switchOnNext Synchronize Take take_with_time takeFirst TakeLast takeLastBuffer takeLastBufferWithTime takeLastWithTime takeRight (see also: TakeLast) TakeUntil takeUntilWithTime TakeWhile take_while_with_index tail tap tapOnCompleted tapOnError tapOnNext Then thenDo Throttle throttleFirst throttleLast throttleWithSelector throttleWithTimeout Throw

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throwError throwException TimeInterval Timeout timeoutWithSelector Timer Timestamp To to_a ToArray ToAsync toBlocking toBuffer to_dict ToDictionary ToEnumerable ToEvent ToEventPattern ToFuture to_h toIndexedSeq toIterable toIterator ToList ToLookup toMap toMultiMap ToObservable toSet toSortedList toStream ToTask toTraversable toVector tumbling tumblingBuffer unsubscribeOn Using When Where while whileDo Window windowWithCount windowWithTime windowWithTimeOrCount windowed withFilter withLatestFrom Zip zipArray zipWith zipWithIndex ++ +: :+

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at a high level, learning Rx reminds me of approaching learning git init clone commit push pull