Awesome

Reactive polyglot

R. (Ramda) stands for standard functional toolkit.

Comparison notes

Operator counterparts aren't and can't be fully equivalent.<br/> "Kinda the same" – is the current definition.

The following projects, were created with different goals and tradeoffs in mind, so every comparison and analogy is subjective and can be argued. The presence of some operator is not necessary good, as well as the abscence is not necessary bad.

Note, that primitives differ for each library. In descriptions, we broadly refer to all the "observable primitives" as streams*, though, technically speaking, some of them are rather stream-like entities.

To find something, search for a term you know.

API

Create

Create an empty stream

• KefirJS: never
• MostJS: empty
• RxJS: of
• XStream: empty

Create a stream from a single value

• KefirJS: constant
• MostJS: of, just
• RxJS: of, just
• XStream: of

Create a stream from an array

• KefirJS: sequentially
• MostJS: from
• RxJS: from, of
• XStream: from, fromArray

Create a stream from a promise

• KefirJS: fromPromise
• MostJS: fromPromise
• RxJS: fromPromise
• XStream: fromPromise

Create a stream from an event

• KefirJS: fromEvents
• MostJS: fromEvent
• RxJS: fromEvent
• XStream: fromEvent

Create a stream from a callback

• KefirJS: stream, fromCallback, fromNodeCallback, fromPoll
• MostJS: new Stream
• RxJS: new Observable, bindCallback, bindNodeCallback
• XStream: ? (make a promise first)

Prepend a stream with a value

• KefirJS: merge + constant
• MostJS: startWith
• RxJS: startWith
• XStream: startWith

Transform (data events)

Map value one-to-one

• KefirJS: map
• MostJS: map, constant
• RxJS: map, mapTo
• XStream: map

Filter value by a predicate

• KefirJS: filter
• MostJS: filter
• RxJS: filter
• XStream: filter

Skip N initial values

• KefirJS: skip
• MostJS: skip
• RxJS: skip
• XStream: drop

Take N initial values

• KefirJS: take
• MostJS: take
• RxJS: take
• XStream: take

Make a value from an accumulator and a next value

• KefirJS: scan
• MostJS: scan
• RxJS: scan
• XStream: fold

Combine

Merge multiple streams together

• KefirJS: merge
• MostJS: merge
• RxJS: merge
• XStream: merge

Pay attention that Kefir's merge accepts arrays while others are variadic.

Combine multiple streams together

• KefirJS: combine
• MostJS: combine
• RxJS: combineLatest
• XStream: combine

Sample a stream by another stream

• KefirJS: combine, sampledBy
• MostJS: sample, sampleWith
• RxJS: sample, withLatestFrom
• XStream: sampleCombine

Chain streams sequentially

• KefirJS: flatMapConcat
• MostJS: concatMap
• RxJS: concatMap
• XStream: map + flattenSequentially

Create

Create stream from non-stream values.

Mapper

Modify events one to one.

Transforms

Modify events * to *.

Filters

Skip events by predicate or signal.

Combinators

Combine multiple streams into single.

Side effects

Produce side effect for every event.

Ending

Operators which target end event somehow.

Concurrency

History

Design diffs

RxJS

1. Three primitives: Observer, Observable, Subject.
2. Observables end on error.
3. Provides API to handle errors.
4. Does not provide API to handle ending.

KefirJS

1. Two primitives: Stream and Property (like XStream).
2. Observables does not end on error (by default).
3. Provides API to handle errors.
4. Provides API to handle ending.

MostJS

1. One primitive: Stream (+ community-driven).
2. Separate packages for subject-like and property-like primitives.
3. Provides API to handle errors.
4. Provides API to handle ending.

XStream

1. Two primitives: Stream and MemoryStream (like KefirJS).
2. Always multicast. A Stream is like an RxJS Subject.
3. Streams end on error.

Common

RxJS does not emit initial scan value as event (use startWith for that).

Rx.Observable.interval(100).map(x => 1)
  .scan(add, 0);
  .subscribe(console.log); // 1--2--3--...

Most.periodic(100, 1)
  .scan(add, 0);
  .observe(console.log); // 0--1--2--3--...

Found docs / API quirks

MostJS

startWith vs sampleWith vs continueWith + recoverWith vs skipRepeatsWith<br/> (val vs none vs func vs stream)

tap is listed in "Transform" section.

RxJS

startWith is listed in "Combine" section.

mergeAll is listed in "Combine" section.

distinct is not listed in "Filtering" section.

takeUntil is not listed in "Filtering" section.

just / return should be deprecated in favor of of.

fromArray should be deprecated in favor of from.

Links

bacon-vs-kefir – BaconJS vs KefirJS API comparison

dataflows – web arch. dataflow comparison

stream-conversions – tool for cross-library stream conversions

Additional Read

https://github.com/cujojs/most/issues/171

https://twitter.com/rpominov/status/689566111734599683

https://github.com/zenparsing/es-observable/issues/66

Reactive polyglot

R. (Ramda) stands for standard functional toolkit.

Comparison notes

Operator counterparts aren't and can't be fully equivalent.<br/> "Kinda the same" – is the current definition.

The following projects, were created with different goals and tradeoffs in mind, so every comparison and analogy is subjective and can be argued. The presence of some operator is not necessary good, as well as the abscence is not necessary bad.

Note, that primitives differ for each library. In descriptions, we broadly refer to all the "observable primitives" as streams*, though, technically speaking, some of them are rather stream-like entities.

To find something, search for a term you know.

API

Create

Create an empty stream

• KefirJS: never
• MostJS: empty
• RxJS: of
• XStream: empty

Create a stream from a single value

• KefirJS: constant
• MostJS: of, just
• RxJS: of, just
• XStream: of

Create a stream from an array

• KefirJS: sequentially
• MostJS: from
• RxJS: from, of
• XStream: from, fromArray

Create a stream from a promise

• KefirJS: fromPromise
• MostJS: fromPromise
• RxJS: fromPromise
• XStream: fromPromise

Create a stream from an event

• KefirJS: fromEvents
• MostJS: fromEvent
• RxJS: fromEvent
• XStream: fromEvent

Create a stream from a callback

• KefirJS: stream, fromCallback, fromNodeCallback, fromPoll
• MostJS: new Stream
• RxJS: new Observable, bindCallback, bindNodeCallback
• XStream: ? (make a promise first)

Prepend a stream with a value

• KefirJS: merge + constant
• MostJS: startWith
• RxJS: startWith
• XStream: startWith

Transform (data events)

Map value one-to-one

• KefirJS: map
• MostJS: map, constant
• RxJS: map, mapTo
• XStream: map

Filter value by a predicate

• KefirJS: filter
• MostJS: filter
• RxJS: filter
• XStream: filter

Skip N initial values

• KefirJS: skip
• MostJS: skip
• RxJS: skip
• XStream: drop

Take N initial values

• KefirJS: take
• MostJS: take
• RxJS: take
• XStream: take

Make a value from an accumulator and a next value

• KefirJS: scan
• MostJS: scan
• RxJS: scan
• XStream: fold

Combine

Merge multiple streams together

• KefirJS: merge
• MostJS: merge
• RxJS: merge
• XStream: merge

Pay attention that Kefir's merge accepts arrays while others are variadic.

Combine multiple streams together

• KefirJS: combine
• MostJS: combine
• RxJS: combineLatest
• XStream: combine

Sample a stream by another stream

• KefirJS: combine, sampledBy
• MostJS: sample, sampleWith
• RxJS: sample, withLatestFrom
• XStream: sampleCombine

Chain streams sequentially

• KefirJS: flatMapConcat
• MostJS: concatMap
• RxJS: concatMap
• XStream: map + flattenSequentially

Create

Create stream from non-stream values.

Mapper

Modify events one to one.

Transforms

Modify events * to *.

Filters

Skip events by predicate or signal.

Combinators

Combine multiple streams into single.

Side effects

Produce side effect for every event.

Ending

Operators which target end event somehow.

Concurrency

History

Design diffs

RxJS

1. Three primitives: Observer, Observable, Subject.
2. Observables end on error.
3. Provides API to handle errors.
4. Does not provide API to handle ending.

KefirJS

1. Two primitives: Stream and Property (like XStream).
2. Observables does not end on error (by default).
3. Provides API to handle errors.
4. Provides API to handle ending.

MostJS

1. One primitive: Stream (+ community-driven).
2. Separate packages for subject-like and property-like primitives.
3. Provides API to handle errors.
4. Provides API to handle ending.

XStream

1. Two primitives: Stream and MemoryStream (like KefirJS).
2. Always multicast. A Stream is like an RxJS Subject.
3. Streams end on error.

Common

RxJS does not emit initial scan value as event (use startWith for that).

Rx.Observable.interval(100).map(x => 1)
  .scan(add, 0);
  .subscribe(console.log); // 1--2--3--...

Most.periodic(100, 1)
  .scan(add, 0);
  .observe(console.log); // 0--1--2--3--...

Found docs / API quirks

MostJS

startWith vs sampleWith vs continueWith + recoverWith vs skipRepeatsWith<br/> (val vs none vs func vs stream)

tap is listed in "Transform" section.

RxJS

startWith is listed in "Combine" section.

mergeAll is listed in "Combine" section.

distinct is not listed in "Filtering" section.

takeUntil is not listed in "Filtering" section.

just / return should be deprecated in favor of of.

fromArray should be deprecated in favor of from.

Links

bacon-vs-kefir – BaconJS vs KefirJS API comparison

dataflows – web arch. dataflow comparison

stream-conversions – tool for cross-library stream conversions

Additional Read

https://github.com/cujojs/most/issues/171

https://twitter.com/rpominov/status/689566111734599683

https://github.com/zenparsing/es-observable/issues/66