Reactive polyglot

R. (Ramda) stands for standard functional toolkit.

Comparison notes

Operator counterparts aren't and can't be fully equivalent.
"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.

KefirJS	MostJS	RxJS	XStream
`interval`	`periodic`	`interval + map`	`periodic`
`repeat`	`of + R.range`	`repeat`	`of + R.range`
`?`	`iterate`	`generate`	?
`?`	`generate`	`generate`	?

Mapper

Modify events one to one.

KefirJS	MostJS	RxJS	XStream
`delay`	`delay`	`delay`	`combine(delay(500))`
`– (map)`	`timestamp`	`timestamp`	`– (map)`

Transforms

Modify events * to *.

MostJS	RxJS	XStream
`chain / flatMap`	`flatMap`	`map + flattenConcurrently`
`map + switch`	`switchMap / flatMapLatest`	`map + flatten`
`join`	`mergeAll`	`flatten`
`loop`	`scan + map`	`fold + map`
`– (custom)`	`bufferWithCount`	?

Filters

Skip events by predicate or signal.

MostJS	RxJS	XStream
`skipRepeats`	`distinctUntilChanged`	`dropRepeats`
`skipRepeatsWith`	`– (scan)`	`dropRepeats`
`slice`	`skip + take`	`drop + take`
`skipWhile`	`skipWhile`	`fold + filter + map`
`takeWhile`	`takeWhile`	`filter + endWhen`
`since / skipUntil`	`skipUntil`	`fold + filter + map`
`until / takeUntil`	`takeUntil`	`filter + endWhen`
`during`	`window + take(1)`	?

Combinators

Combine multiple streams into single.

MostJS	RxJS	XStream
`zip`	`zip`	?
`concat`	`concat`	`concat`
`ap`	`combineLatest`	?

Side effects

Produce side effect for every event.

MostJS	RxJS	XStream
`tap`	`do / tap`	`debug`

Ending

Operators which target end event somehow.

MostJS	RxJS	XStream
`empty`	`empty`	`empty`
`never`	`never`	`never`
`continueWith`	`?`	`concat`

Concurrency

MostJS	RxJS
`– (custom)`	`amb / race`

History

MostJS	RxJS
`– (custom)`

Design diffs

RxJS

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

KefirJS

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

MostJS

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

XStream

Two primitives: Stream and MemoryStream (like KefirJS).
Always multicast. A Stream is like an RxJS Subject.
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
(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

cujojs/most#171

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

tc39/proposal-observable#66

Reactive polyglot

R. (Ramda) stands for standard functional toolkit.

Comparison notes

Operator counterparts aren't and can't be fully equivalent.
"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.

KefirJS	MostJS	RxJS	XStream
`interval`	`periodic`	`interval + map`	`periodic`
`repeat`	`of + R.range`	`repeat`	`of + R.range`
`?`	`iterate`	`generate`	?
`?`	`generate`	`generate`	?

Mapper

Modify events one to one.

KefirJS	MostJS	RxJS	XStream
`delay`	`delay`	`delay`	`combine(delay(500))`
`– (map)`	`timestamp`	`timestamp`	`– (map)`

Transforms

Modify events * to *.

MostJS	RxJS	XStream
`chain / flatMap`	`flatMap`	`map + flattenConcurrently`
`map + switch`	`switchMap / flatMapLatest`	`map + flatten`
`join`	`mergeAll`	`flatten`
`loop`	`scan + map`	`fold + map`
`– (custom)`	`bufferWithCount`	?

Filters

Skip events by predicate or signal.

MostJS	RxJS	XStream
`skipRepeats`	`distinctUntilChanged`	`dropRepeats`
`skipRepeatsWith`	`– (scan)`	`dropRepeats`
`slice`	`skip + take`	`drop + take`
`skipWhile`	`skipWhile`	`fold + filter + map`
`takeWhile`	`takeWhile`	`filter + endWhen`
`since / skipUntil`	`skipUntil`	`fold + filter + map`
`until / takeUntil`	`takeUntil`	`filter + endWhen`
`during`	`window + take(1)`	?

Combinators

Combine multiple streams into single.

MostJS	RxJS	XStream
`zip`	`zip`	?
`concat`	`concat`	`concat`
`ap`	`combineLatest`	?

Side effects

Produce side effect for every event.

MostJS	RxJS	XStream
`tap`	`do / tap`	`debug`

Ending

Operators which target end event somehow.

MostJS	RxJS	XStream
`empty`	`empty`	`empty`
`never`	`never`	`never`
`continueWith`	`?`	`concat`

Concurrency

MostJS	RxJS
`– (custom)`	`amb / race`

History

MostJS	RxJS
`– (custom)`

Design diffs

RxJS

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

KefirJS

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

MostJS

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

XStream

Two primitives: Stream and MemoryStream (like KefirJS).
Always multicast. A Stream is like an RxJS Subject.
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
(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

cujojs/most#171

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

tc39/proposal-observable#66

Files

README.md

Latest commit

History

README.md

File metadata and controls

Reactive polyglot

Comparison notes

API

Create

Create an empty stream

Create a stream from a single value

Create a stream from an array

Create a stream from a promise

Create a stream from an event

Create a stream from a callback

Prepend a stream with a value

Transform (data events)

Map value one-to-one

Filter value by a predicate

Skip N initial values

Take N initial values

Make a value from an accumulator and a next value

Combine

Merge multiple streams together

Combine multiple streams together

Sample a stream by another stream

Chain streams sequentially

Create

Mapper

Transforms

Filters

Combinators

Side effects

Ending

Concurrency

History

Design diffs

RxJS

KefirJS

MostJS

XStream

Common

Found docs / API quirks

MostJS

RxJS

Links

Additional Read

Reactive polyglot

Comparison notes

API

Create

Create an empty stream

Create a stream from a single value

Create a stream from an array

Create a stream from a promise

Create a stream from an event

Create a stream from a callback

Prepend a stream with a value

Transform (data events)

Map value one-to-one

Filter value by a predicate

Skip N initial values

Take N initial values

Make a value from an accumulator and a next value

Combine

Merge multiple streams together

Combine multiple streams together

Sample a stream by another stream

Chain streams sequentially

Create

Mapper

Transforms

Filters

Combinators

Side effects

Ending

Concurrency

History

Design diffs