├── dummy.js
├── bufferWithCount.md
├── history.md
└── README.md


/dummy.js:
--------------------------------------------------------------------------------
1 | // Tells GitHub this repo is about JavaScript
2 | 


--------------------------------------------------------------------------------
/bufferWithCount.md:
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 1 | ### Buffer every N events and emit as single event
 2 | 
 3 | ```js
 4 | import Most from "most";
 5 | import {add, append, curry, takeLast} from "ramda";
 6 | 
 7 | // Number -> Stream a -> Stream [a]
 8 | let buffer = curry((n, s$) => {
 9 |   return s$
10 |     .loop((memo, item) => {
11 |       let value = takeLast(n, append(item, memo));
12 |       let seed = value.length == n ? [] : value;
13 |       return {seed, value};
14 |     }, [])
15 |     .filter(x => x.length == n)
16 | });
17 | 
18 | let s$ = Most
19 |   .periodic(100, 1)
20 |   .scan(add, 0); // 0--1--2--...
21 | 
22 | buffer(3, s$) // [0, 1, 2]--[3, 4, 5]--...
23 |   .observe(console.log); 
24 | ```
25 | 


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/history.md:
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 1 | ### Track history for N events
 2 | 
 3 | #### RxJS
 4 | 
 5 | ```js
 6 | let {append, drop, repeat} = require("ramda")
 7 | 
 8 | let appendSliding = curry((n, x, xs) => {
 9 |   let ys = append(x, xs)
10 |   if (ys.length > n) {
11 |     return drop(ys.length - n, ys)
12 |   } else {
13 |     return ys
14 |   }
15 | })
16 | 
17 | let history = function (n) {
18 |   if (n <= 0) {
19 |     throw Error("n must be an unsigned integer, got "+ String(n))
20 |   }
21 |   let put = appendSliding(n)
22 |   return this.scan((stateHistory, newState) => {
23 |     return put(newState, stateHistory)
24 |   }, repeat(null, n))
25 | }
26 | 
27 | // Usage
28 | statefulStream
29 |   ::history(3)
30 | ```
31 | 


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/README.md:
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  1 | # Reactive polyglot
  2 | 
  3 | **`R.`** [(Ramda)](http://ramdajs.com/0.19.1/index.html) stands for standard functional toolkit.
  4 | 
  5 | ### Comparison notes
  6 | 
  7 | Operator counterparts aren't and can't be fully equivalent.<br/>
  8 | "Kinda the same" – is the current definition.
  9 | 
 10 | The following projects, were created with different goals and tradeoffs in mind, so every comparison
 11 | and analogy is subjective and can be argued. The presence of some operator is not necessary good, as
 12 | well as the abscence is not necessary bad.
 13 | 
 14 | Note, that primitives differ for each library. In descriptions, we broadly refer to all the "observable
 15 | primitives" as **streams***, though, technically speaking, some of them are rather stream-like entities.
 16 | 
 17 | To find something, search for a term you know.
 18 | 
 19 | ## API
 20 | 
 21 | ### Create
 22 | 
 23 | #### Create an empty stream
 24 | 
 25 | * KefirJS: [`never`](http://kefirjs.github.io/kefir/#never)
 26 | * MostJS: [`empty`](https://github.com/cujojs/most/blob/master/docs/api.md#mostempty)
 27 | * RxJS: [`of`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/of.md)
 28 | * XStream: [`empty`](https://github.com/staltz/xstream#of)
 29 | 
 30 | #### Create a stream from a single value
 31 | 
 32 | * KefirJS: [`constant`](http://kefirjs.github.io/kefir/#constant)
 33 | * MostJS: [`of`](https://github.com/cujojs/most/blob/master/docs/api.md#mostjust), [`just`](https://github.com/cujojs/most/blob/master/docs/api.md#mostjust)
 34 | * RxJS: [`of`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/of.md), [`just`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/return.md)
 35 | * XStream: [`of`](https://github.com/staltz/xstream#of)
 36 | 
 37 | #### Create a stream from an array
 38 | 
 39 | * KefirJS: [`sequentially`](http://kefirjs.github.io/kefir/#sequentially)
 40 | * MostJS: [`from`](https://github.com/cujojs/most/blob/master/docs/api.md#mostfrom)
 41 | * RxJS: [`from`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/from.md), [`of`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/of.md)
 42 | * XStream: [`from`](https://github.com/staltz/xstream#from), [`fromArray`](https://github.com/staltz/xstream#fromArray)
 43 | 
 44 | #### Create a stream from a promise
 45 | 
 46 | * KefirJS: [`fromPromise`](http://kefirjs.github.io/kefir/#from-promise)
 47 | * MostJS: [`fromPromise`](https://github.com/cujojs/most/blob/master/docs/api.md#mostfrompromise)
 48 | * RxJS: [`fromPromise`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/frompromise.md)
 49 | * XStream: [`fromPromise`](https://github.com/staltz/xstream#fromPromise)
 50 | 
 51 | #### Create a stream from an event
 52 | 
 53 | * KefirJS: [`fromEvents`](http://kefirjs.github.io/kefir/#from-event)
 54 | * MostJS: [`fromEvent`](https://github.com/cujojs/most/blob/master/docs/api.md#mostfromevent)
 55 | * RxJS: [`fromEvent`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/fromevent.md)
 56 | * XStream: [`fromEvent`](https://github.com/staltz/xstream/blob/master/EXTRA_DOCS.md#fromEvent)
 57 | 
 58 | #### Create a stream from a callback
 59 | 
 60 | * KefirJS: [`stream`](http://kefirjs.github.io/kefir/#stream), [`fromCallback`](http://kefirjs.github.io/kefir/#from-callback), [`fromNodeCallback`](http://kefirjs.github.io/kefir/#from-node-callback), [`fromPoll`](http://kefirjs.github.io/kefir/#from-poll)
 61 | * MostJS: `new Stream`
 62 | * RxJS: `new Observable`, `bindCallback`, `bindNodeCallback`
 63 | * XStream: `? (make a promise first)`
 64 | 
 65 | #### Prepend a stream with a value
 66 | 
 67 | * KefirJS: [`merge`](http://kefirjs.github.io/kefir/#merge) `+` [`constant`](http://kefirjs.github.io/kefir/#constant)
 68 | * MostJS: `startWith`
 69 | * RxJS: [`startWith`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/startwith.md)
 70 | * XStream: `startWith`
 71 | 
 72 | ### Transform (data events)
 73 | 
 74 | #### Map value one-to-one
 75 | 
 76 | * KefirJS: [`map`](http://kefirjs.github.io/kefir/#map)
 77 | * MostJS: `map`, `constant`
 78 | * RxJS: [`map`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/select.md), `mapTo`
 79 | * XStream: `map`
 80 | 
 81 | #### Filter value by a predicate
 82 | 
 83 | * KefirJS: [`filter`](http://kefirjs.github.io/kefir/#filter)
 84 | * MostJS: `filter`
 85 | * RxJS: [`filter`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/where.md)
 86 | * XStream: `filter`
 87 | 
 88 | #### Skip N initial values
 89 | 
 90 | * KefirJS: [`skip`](http://kefirjs.github.io/kefir/#skip)
 91 | * MostJS: `skip`
 92 | * RxJS: [`skip`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/skip.md)
 93 | * XStream: `drop`
 94 | 
 95 | #### Take N initial values
 96 | 
 97 | * KefirJS: [`take`](http://kefirjs.github.io/kefir/#take)
 98 | * MostJS: `take`
 99 | * RxJS: [`take`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/take.md)
100 | * XStream: `take`
101 | 
102 | #### Make a value from an accumulator and a next value
103 | 
104 | * KefirJS: [`scan`](http://kefirjs.github.io/kefir/#scan)
105 | * MostJS: `scan`
106 | * RxJS: [`scan`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/scan.md)
107 | * XStream: `fold`
108 | 
109 | ### Combine
110 | 
111 | #### Merge multiple streams together
112 | 
113 | * KefirJS: [`merge`](http://kefirjs.github.io/kefir/#merge)
114 | * MostJS: `merge`
115 | * RxJS: [`merge`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/merge.md)
116 | * XStream: `merge`
117 | 
118 | Pay attention that Kefir's `merge` accepts arrays while others are variadic.
119 | 
120 | #### Combine multiple streams together
121 | 
122 | * KefirJS: [`combine`](http://kefirjs.github.io/kefir/#combine)
123 | * MostJS: `combine`
124 | * RxJS: [`combineLatest`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/combinelatest.md)
125 | * XStream: `combine`
126 | 
127 | #### Sample a stream by another stream
128 | 
129 | * KefirJS: [`combine`](http://kefirjs.github.io/kefir/#combine), [`sampledBy`](http://kefirjs.github.io/kefir/#obs-sampled-by)
130 | * MostJS: `sample`, `sampleWith`
131 | * RxJS: [`sample`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/sample.md), [`withLatestFrom`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/withlatestfrom.md)
132 | * XStream: `sampleCombine`
133 | 
134 | #### Chain streams sequentially
135 | 
136 | * KefirJS: [`flatMapConcat`](http://kefirjs.github.io/kefir/#flat-map-concat)
137 | * MostJS: [`concatMap`](https://github.com/cujojs/most/blob/master/docs/api.md#concatmap)
138 | * RxJS: [`concatMap`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/concatmap.md)
139 | * XStream: `map + flattenSequentially`
140 | 
141 | ---
142 | 
143 | ### Create
144 | 
145 | Create stream from non-stream values.
146 | 
147 | <table>
148 | <tr>
149 |   <th>KefirJS</th>
150 |   <th>MostJS</th>
151 |   <th>RxJS</th>
152 |   <th>XStream</th>
153 | </tr>
154 | <tr>
155 |   <td><code>interval</code></td>
156 |   <td><code>periodic</code></td>
157 |   <td><code>interval + map</code></td>
158 |   <td><code>periodic</code></td>
159 | </tr>
160 | <tr>
161 |   <td><code>repeat</code></td>
162 |   <td><code>of + R.range</code></td>
163 |   <td><code>repeat</code></td>
164 |   <td><code>of + R.range</code></td>
165 | </tr>
166 | <tr>
167 |   <td><code>?</code></td>
168 |   <td><code>iterate</code></td>
169 |   <td><code>generate</code></td>
170 |   <td>?</td>
171 | </tr>
172 | <tr>
173 |   <td><code>?</code></td>
174 |   <td><code>generate</code></td>
175 |   <td><code>generate</code></td>
176 |   <td>?</td>
177 | </tr>
178 | </table>
179 | 
180 | ### Mapper
181 | 
182 | Modify events one to one.
183 | 
184 | <table>
185 | <tr>
186 |   <th>KefirJS</th>
187 |   <th>MostJS</th>
188 |   <th>RxJS</th>
189 |   <th>XStream</th>
190 | </tr>
191 | <tr>
192 |   <td><code>delay</code></td>
193 |   <td><code>delay</code></td>
194 |   <td><code>delay</code></td>
195 |   <td><code>combine(delay(500))</code></td>
196 | </tr>
197 | <tr>
198 |   <td><code>– (map)</code></td>
199 |   <td><code>timestamp</code></td>
200 |   <td><code>timestamp</code></td>
201 |   <td><code>– (map)</code></td>
202 | </tr>
203 | </table>
204 | 
205 | ### Transforms
206 | 
207 | Modify events * to *.
208 | 
209 | <table>
210 | <tr>
211 |   <th>MostJS</th>
212 |   <th>RxJS</th>
213 |   <th>XStream</th>
214 | </tr>
215 | <tr>
216 |   <td><code>chain / flatMap</code></td>
217 |   <td><code>flatMap</code></td>
218 |   <td><code>map + flattenConcurrently</code></td>
219 | </tr>
220 | <tr>
221 |   <td><code>map + switch</code></td>
222 |   <td><code>switchMap / flatMapLatest</code></td>
223 |   <td><code>map + flatten</code></td>
224 | </tr>
225 | <tr>
226 |   <td><code>join</code></td>
227 |   <td><code>mergeAll</code></td>
228 |   <td><code>flatten</code></td>
229 | </tr>
230 | <tr>
231 |   <td><code>loop</code></td>
232 |   <td><code>scan + map</code></td>
233 |   <td><code>fold + map</code></td>
234 | </tr>
235 | <tr>
236 |   <td><code>– (<a href="bufferWithCount.md">custom</a>)</code></td>
237 |   <td><code>bufferWithCount</code></td>
238 |   <td>?</td>
239 | </tr>
240 | </table>
241 | 
242 | ### Filters
243 | 
244 | Skip events by predicate or signal.
245 | 
246 | <table>
247 | <tr>
248 |   <th>MostJS</th>
249 |   <th>RxJS</th>
250 |   <th>XStream</th>
251 | </tr>
252 | <tr>
253 |   <td><code>skipRepeats</code></td>
254 |   <td><code>distinctUntilChanged</code></td>
255 |   <td><code>dropRepeats</code></td>
256 | </tr>
257 | <tr>
258 |   <td><code>skipRepeatsWith</code></td>
259 |   <td><code>– (scan)</code></td>
260 |   <td><code>dropRepeats</code></td>
261 | </tr>
262 | <tr>
263 |   <td><code>slice</code></td>
264 |   <td><code>skip + take</code></td>
265 |   <td><code>drop + take</code></td>
266 | </tr>
267 | <tr>
268 |   <td><code>skipWhile</code></td>
269 |   <td><code>skipWhile</code></td>
270 |   <td><code>fold + filter + map</code></td>
271 | </tr>
272 | <tr>
273 |   <td><code>takeWhile</code></td>
274 |   <td><code>takeWhile</code></td>
275 |   <td><code>filter + endWhen</code></td>
276 | </tr>
277 | <tr>
278 |   <td><code>since / skipUntil</code></td>
279 |   <td><code>skipUntil</code></td>
280 |   <td><code>fold + filter + map</code></td>
281 | </tr>
282 | <tr>
283 |   <td><code>until / takeUntil</code></td>
284 |   <td><code>takeUntil</code></td>
285 |   <td><code>filter + endWhen</code></td>
286 | </tr>
287 | <tr>
288 |   <td><code>during</code></td>
289 |   <td><code>window + take(1)</code></td>
290 |   <td>?</td>
291 | </tr>
292 | </table>
293 | 
294 | ### Combinators
295 | 
296 | Combine multiple streams into single.
297 | 
298 | <table>
299 | <tr>
300 |   <th>MostJS</th>
301 |   <th>RxJS</th>
302 |   <th>XStream</th>
303 | </tr>
304 | <tr>
305 |   <td><code>zip</code></td>
306 |   <td><code>zip</code></td>
307 |   <td>?</td>
308 | </tr>
309 | <tr>
310 |   <td><code>concat</code></td>
311 |   <td><code>concat</code></td>
312 |   <td><code>concat</code></td>
313 | </tr>
314 | <tr>
315 |   <td><code>ap</code></td>
316 |   <td><code>combineLatest</code></td>
317 |   <td>?</td>
318 | </tr>
319 | </table>
320 | 
321 | ### Side effects
322 | 
323 | Produce side effect for every event.
324 | 
325 | <table>
326 | <tr>
327 |   <th>MostJS</th>
328 |   <th>RxJS</th>
329 |   <th>XStream</th>
330 | </tr>
331 | <tr>
332 |   <td><code>tap</code></td>
333 |   <td><code>do / tap</code></td>
334 |   <td><code>debug</code></td>
335 | </tr>
336 | </table>
337 | 
338 | ### Ending
339 | 
340 | Operators which target **end** event somehow.
341 | 
342 | <table>
343 | <tr>
344 |   <th>MostJS</th>
345 |   <th>RxJS</th>
346 |   <th>XStream</th>
347 | </tr>
348 | <tr>
349 |   <td><code>empty</code></td>
350 |   <td><code>empty</code></td>
351 |   <td><code>empty</code></td>
352 | </tr>
353 | <tr>
354 |   <td><code>never</code></td>
355 |   <td><code>never</code></td>
356 |   <td><code>never</code></td>
357 | </tr>
358 | <tr>
359 |   <td><code>continueWith</code></td>
360 |   <td><code>?</code></td>
361 |   <td><code>concat</code></td>
362 | </tr>
363 | </table>
364 | 
365 | ### Concurrency
366 | 
367 | <table>
368 | <tr>
369 |   <th>MostJS</th>
370 |   <th>RxJS</th>
371 | </tr>
372 | <tr>
373 |   <td><code>– (<a href="https://github.com/ivan-kleshnin/reactive-polyglot/wiki/race">custom</a>)</code></td>
374 |   <td><code>amb / race</code></td>
375 | </tr>
376 | </table>
377 | 
378 | ### History
379 | 
380 | <table>
381 | <tr>
382 |   <th>MostJS</th>
383 |   <th>RxJS</th>
384 | </tr>
385 | <tr>
386 |   <td colspan="2"><code>– (<a href="history.md">custom</a>)</code></td>
387 | </tr>
388 | </table>
389 | 
390 | ### Design diffs
391 | 
392 | #### RxJS
393 | 
394 | 1. Three primitives: `Observer`, `Observable`, `Subject`.
395 | 2. Observables end on error.
396 | 3. Provides API to handle errors.
397 | 3. Does not provide API to handle ending.
398 | 
399 | #### KefirJS
400 | 
401 | 1. Two primitives: `Stream` and `Property` (like XStream).
402 | 2. Observables does not end on error (by default).
403 | 3. Provides API to handle errors.
404 | 4. Provides API to handle ending.
405 | 
406 | #### MostJS
407 | 
408 | 1. One primitive: `Stream` (+ community-driven).
409 | 2. Separate packages for [subject-like](https://github.com/TylorS/most-subject) and [property-like](https://github.com/mostjs/hold) primitives.
410 | 3. Provides API to handle errors.
411 | 4. Provides API to handle ending.
412 | 
413 | #### XStream
414 | 
415 | 1. Two primitives: `Stream` and `MemoryStream` (like KefirJS).
416 | 2. Always multicast. A Stream is like an RxJS Subject.
417 | 3. Streams end on error.
418 | 
419 | #### Common
420 | 
421 | RxJS does not emit initial `scan` value as event (use `startWith` for that).
422 | 
423 | ```js
424 | Rx.Observable.interval(100).map(x => 1)
425 |   .scan(add, 0);
426 |   .subscribe(console.log); // 1--2--3--...
427 | 
428 | Most.periodic(100, 1)
429 |   .scan(add, 0);
430 |   .observe(console.log); // 0--1--2--3--...
431 | ```
432 | 
433 | ### Found docs / API quirks
434 | 
435 | #### MostJS
436 | 
437 | `startWith` vs `sampleWith` vs `continueWith` + `recoverWith` vs `skipRepeatsWith`<br/>
438 | (val vs none vs func vs stream)
439 | 
440 | `tap` is listed in "Transform" section.
441 | 
442 | #### RxJS
443 | 
444 | `startWith` is listed in "Combine" section.
445 | 
446 | `mergeAll` is listed in "Combine" section.
447 | 
448 | `distinct` is not listed in "Filtering" section.
449 | 
450 | `takeUntil` is not listed in "Filtering" section.
451 | 
452 | `just` / `return` should be deprecated in favor of `of`.
453 | 
454 | `fromArray` should be deprecated in favor of `from`.
455 | 
456 | ### Links
457 | 
458 | [bacon-vs-kefir](https://github.com/rpominov/kefir/blob/master/bacon-vs-kefir-api.md) – BaconJS vs KefirJS API comparison
459 | 
460 | [dataflows](https://github.com/ivan-kleshnin/dataflows) – web arch. dataflow comparison
461 | 
462 | [stream-conversions](https://github.com/TylorS/stream-conversions) – tool for cross-library stream conversions
463 | 
464 | ### Additional Read
465 | 
466 | https://github.com/cujojs/most/issues/171
467 | 
468 | https://twitter.com/rpominov/status/689566111734599683
469 | 
470 | https://github.com/zenparsing/es-observable/issues/66
471 | 
472 | # Reactive polyglot
473 | 
474 | **`R.`** [(Ramda)](http://ramdajs.com/0.19.1/index.html) stands for standard functional toolkit.
475 | 
476 | ### Comparison notes
477 | 
478 | Operator counterparts aren't and can't be fully equivalent.<br/>
479 | "Kinda the same" – is the current definition.
480 | 
481 | The following projects, were created with different goals and tradeoffs in mind, so every comparison
482 | and analogy is subjective and can be argued. The presence of some operator is not necessary good, as
483 | well as the abscence is not necessary bad.
484 | 
485 | Note, that primitives differ for each library. In descriptions, we broadly refer to all the "observable
486 | primitives" as **streams***, though, technically speaking, some of them are rather stream-like entities.
487 | 
488 | To find something, search for a term you know.
489 | 
490 | ## API
491 | 
492 | ### Create
493 | 
494 | #### Create an empty stream
495 | 
496 | * KefirJS: [`never`](http://kefirjs.github.io/kefir/#never)
497 | * MostJS: [`empty`](https://github.com/cujojs/most/blob/master/docs/api.md#mostempty)
498 | * RxJS: [`of`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/of.md)
499 | * XStream: [`empty`](https://github.com/staltz/xstream#of)
500 | 
501 | #### Create a stream from a single value
502 | 
503 | * KefirJS: [`constant`](http://kefirjs.github.io/kefir/#constant)
504 | * MostJS: [`of`](https://github.com/cujojs/most/blob/master/docs/api.md#mostjust), [`just`](https://github.com/cujojs/most/blob/master/docs/api.md#mostjust)
505 | * RxJS: [`of`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/of.md), [`just`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/return.md)
506 | * XStream: [`of`](https://github.com/staltz/xstream#of)
507 | 
508 | #### Create a stream from an array
509 | 
510 | * KefirJS: [`sequentially`](http://kefirjs.github.io/kefir/#sequentially)
511 | * MostJS: [`from`](https://github.com/cujojs/most/blob/master/docs/api.md#mostfrom)
512 | * RxJS: [`from`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/from.md), [`of`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/of.md)
513 | * XStream: [`from`](https://github.com/staltz/xstream#from), [`fromArray`](https://github.com/staltz/xstream#fromArray)
514 | 
515 | #### Create a stream from a promise
516 | 
517 | * KefirJS: [`fromPromise`](http://kefirjs.github.io/kefir/#from-promise)
518 | * MostJS: [`fromPromise`](https://github.com/cujojs/most/blob/master/docs/api.md#mostfrompromise)
519 | * RxJS: [`fromPromise`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/frompromise.md)
520 | * XStream: [`fromPromise`](https://github.com/staltz/xstream#fromPromise)
521 | 
522 | #### Create a stream from an event
523 | 
524 | * KefirJS: [`fromEvents`](http://kefirjs.github.io/kefir/#from-event)
525 | * MostJS: [`fromEvent`](https://github.com/cujojs/most/blob/master/docs/api.md#mostfromevent)
526 | * RxJS: [`fromEvent`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/fromevent.md)
527 | * XStream: [`fromEvent`](https://github.com/staltz/xstream/blob/master/EXTRA_DOCS.md#fromEvent)
528 | 
529 | #### Create a stream from a callback
530 | 
531 | * KefirJS: [`stream`](http://kefirjs.github.io/kefir/#stream), [`fromCallback`](http://kefirjs.github.io/kefir/#from-callback), [`fromNodeCallback`](http://kefirjs.github.io/kefir/#from-node-callback), [`fromPoll`](http://kefirjs.github.io/kefir/#from-poll)
532 | * MostJS: `new Stream`
533 | * RxJS: `new Observable`, `bindCallback`, `bindNodeCallback`
534 | * XStream: `? (make a promise first)`
535 | 
536 | #### Prepend a stream with a value
537 | 
538 | * KefirJS: [`merge`](http://kefirjs.github.io/kefir/#merge) `+` [`constant`](http://kefirjs.github.io/kefir/#constant)
539 | * MostJS: `startWith`
540 | * RxJS: `startWith`
541 | * XStream: `startWith`
542 | 
543 | ### Transform (data events)
544 | 
545 | #### Map value one-to-one
546 | 
547 | * KefirJS: [`map`](http://kefirjs.github.io/kefir/#map)
548 | * MostJS: `map`, `constant`
549 | * RxJS: `map`, `mapTo`
550 | * XStream: `map`
551 | 
552 | #### Filter value by a predicate
553 | 
554 | * KefirJS: [`filter`](http://kefirjs.github.io/kefir/#filter)
555 | * MostJS: `filter`
556 | * RxJS: `filter`
557 | * XStream: `filter`
558 | 
559 | #### Skip N initial values
560 | 
561 | * KefirJS: [`skip`](http://kefirjs.github.io/kefir/#skip)
562 | * MostJS: `skip`
563 | * RxJS: `skip`
564 | * XStream: `drop`
565 | 
566 | #### Take N initial values
567 | 
568 | * KefirJS: [`take`](http://kefirjs.github.io/kefir/#take)
569 | * MostJS: `take`
570 | * RxJS: `take`
571 | * XStream: `take`
572 | 
573 | #### Make a value from an accumulator and a next value
574 | 
575 | * KefirJS: [`scan`](http://kefirjs.github.io/kefir/#scan)
576 | * MostJS: `scan`
577 | * RxJS: `scan`
578 | * XStream: `fold`
579 | 
580 | ### Combine
581 | 
582 | #### Merge multiple streams together
583 | 
584 | * KefirJS: [`merge`](http://kefirjs.github.io/kefir/#merge)
585 | * MostJS: `merge`
586 | * RxJS: `merge`
587 | * XStream: `merge`
588 | 
589 | Pay attention that Kefir's `merge` accepts arrays while others are variadic.
590 | 
591 | #### Combine multiple streams together
592 | 
593 | * KefirJS: [`combine`](http://kefirjs.github.io/kefir/#combine)
594 | * MostJS: `combine`
595 | * RxJS: `combineLatest`
596 | * XStream: `combine`
597 | 
598 | #### Sample a stream by another stream
599 | 
600 | * KefirJS: [`combine`](http://kefirjs.github.io/kefir/#combine), [`sampledBy`](http://kefirjs.github.io/kefir/#obs-sampled-by)
601 | * MostJS: `sample`, `sampleWith`
602 | * RxJS: `sample`, `withLatestFrom`
603 | * XStream: `sampleCombine`
604 | 
605 | #### Chain streams sequentially
606 | 
607 | * KefirJS: [`flatMapConcat`](http://kefirjs.github.io/kefir/#flat-map-concat)
608 | * MostJS: `concatMap`
609 | * RxJS: `concatMap`
610 | * XStream: `map + flattenSequentially`
611 | 
612 | ---
613 | 
614 | ### Create
615 | 
616 | Create stream from non-stream values.
617 | 
618 | <table>
619 | <tr>
620 |   <th>KefirJS</th>
621 |   <th>MostJS</th>
622 |   <th>RxJS</th>
623 |   <th>XStream</th>
624 | </tr>
625 | <tr>
626 |   <td><code>interval</code></td>
627 |   <td><code>periodic</code></td>
628 |   <td><code>interval + map</code></td>
629 |   <td><code>periodic</code></td>
630 | </tr>
631 | <tr>
632 |   <td><code>repeat</code></td>
633 |   <td><code>of + R.range</code></td>
634 |   <td><code>repeat</code></td>
635 |   <td><code>of + R.range</code></td>
636 | </tr>
637 | <tr>
638 |   <td><code>?</code></td>
639 |   <td><code>iterate</code></td>
640 |   <td><code>generate</code></td>
641 |   <td>?</td>
642 | </tr>
643 | <tr>
644 |   <td><code>?</code></td>
645 |   <td><code>generate</code></td>
646 |   <td><code>generate</code></td>
647 |   <td>?</td>
648 | </tr>
649 | </table>
650 | 
651 | ### Mapper
652 | 
653 | Modify events one to one.
654 | 
655 | <table>
656 | <tr>
657 |   <th>KefirJS</th>
658 |   <th>MostJS</th>
659 |   <th>RxJS</th>
660 |   <th>XStream</th>
661 | </tr>
662 | <tr>
663 |   <td><code>delay</code></td>
664 |   <td><code>delay</code></td>
665 |   <td><code>delay</code></td>
666 |   <td><code>combine(delay(500))</code></td>
667 | </tr>
668 | <tr>
669 |   <td><code>– (map)</code></td>
670 |   <td><code>timestamp</code></td>
671 |   <td><code>timestamp</code></td>
672 |   <td><code>– (map)</code></td>
673 | </tr>
674 | </table>
675 | 
676 | ### Transforms
677 | 
678 | Modify events * to *.
679 | 
680 | <table>
681 | <tr>
682 |   <th>MostJS</th>
683 |   <th>RxJS</th>
684 |   <th>XStream</th>
685 | </tr>
686 | <tr>
687 |   <td><code>chain / flatMap</code></td>
688 |   <td><code>flatMap</code></td>
689 |   <td><code>map + flattenConcurrently</code></td>
690 | </tr>
691 | <tr>
692 |   <td><code>map + switch</code></td>
693 |   <td><code>switchMap / flatMapLatest</code></td>
694 |   <td><code>map + flatten</code></td>
695 | </tr>
696 | <tr>
697 |   <td><code>join</code></td>
698 |   <td><code>mergeAll</code></td>
699 |   <td><code>flatten</code></td>
700 | </tr>
701 | <tr>
702 |   <td><code>loop</code></td>
703 |   <td><code>scan + map</code></td>
704 |   <td><code>fold + map</code></td>
705 | </tr>
706 | <tr>
707 |   <td><code>– (<a href="bufferWithCount.md">custom</a>)</code></td>
708 |   <td><code>bufferWithCount</code></td>
709 |   <td>?</td>
710 | </tr>
711 | </table>
712 | 
713 | ### Filters
714 | 
715 | Skip events by predicate or signal.
716 | 
717 | <table>
718 | <tr>
719 |   <th>MostJS</th>
720 |   <th>RxJS</th>
721 |   <th>XStream</th>
722 | </tr>
723 | <tr>
724 |   <td><code>skipRepeats</code></td>
725 |   <td><code>distinctUntilChanged</code></td>
726 |   <td><code>dropRepeats</code></td>
727 | </tr>
728 | <tr>
729 |   <td><code>skipRepeatsWith</code></td>
730 |   <td><code>– (scan)</code></td>
731 |   <td><code>dropRepeats</code></td>
732 | </tr>
733 | <tr>
734 |   <td><code>slice</code></td>
735 |   <td><code>skip + take</code></td>
736 |   <td><code>drop + take</code></td>
737 | </tr>
738 | <tr>
739 |   <td><code>skipWhile</code></td>
740 |   <td><code>skipWhile</code></td>
741 |   <td><code>fold + filter + map</code></td>
742 | </tr>
743 | <tr>
744 |   <td><code>takeWhile</code></td>
745 |   <td><code>takeWhile</code></td>
746 |   <td><code>filter + endWhen</code></td>
747 | </tr>
748 | <tr>
749 |   <td><code>since / skipUntil</code></td>
750 |   <td><code>skipUntil</code></td>
751 |   <td><code>fold + filter + map</code></td>
752 | </tr>
753 | <tr>
754 |   <td><code>until / takeUntil</code></td>
755 |   <td><code>takeUntil</code></td>
756 |   <td><code>filter + endWhen</code></td>
757 | </tr>
758 | <tr>
759 |   <td><code>during</code></td>
760 |   <td><code>window + take(1)</code></td>
761 |   <td>?</td>
762 | </tr>
763 | </table>
764 | 
765 | ### Combinators
766 | 
767 | Combine multiple streams into single.
768 | 
769 | <table>
770 | <tr>
771 |   <th>MostJS</th>
772 |   <th>RxJS</th>
773 |   <th>XStream</th>
774 | </tr>
775 | <tr>
776 |   <td><code>zip</code></td>
777 |   <td><code>zip</code></td>
778 |   <td>?</td>
779 | </tr>
780 | <tr>
781 |   <td><code>concat</code></td>
782 |   <td><code>concat</code></td>
783 |   <td><code>concat</code></td>
784 | </tr>
785 | <tr>
786 |   <td><code>ap</code></td>
787 |   <td><code>combineLatest</code></td>
788 |   <td>?</td>
789 | </tr>
790 | </table>
791 | 
792 | ### Side effects
793 | 
794 | Produce side effect for every event.
795 | 
796 | <table>
797 | <tr>
798 |   <th>MostJS</th>
799 |   <th>RxJS</th>
800 |   <th>XStream</th>
801 | </tr>
802 | <tr>
803 |   <td><code>tap</code></td>
804 |   <td><code>do / tap</code></td>
805 |   <td><code>debug</code></td>
806 | </tr>
807 | </table>
808 | 
809 | ### Ending
810 | 
811 | Operators which target **end** event somehow.
812 | 
813 | <table>
814 | <tr>
815 |   <th>MostJS</th>
816 |   <th>RxJS</th>
817 |   <th>XStream</th>
818 | </tr>
819 | <tr>
820 |   <td><code>empty</code></td>
821 |   <td><code>empty</code></td>
822 |   <td><code>empty</code></td>
823 | </tr>
824 | <tr>
825 |   <td><code>never</code></td>
826 |   <td><code>never</code></td>
827 |   <td><code>never</code></td>
828 | </tr>
829 | <tr>
830 |   <td><code>continueWith</code></td>
831 |   <td><code>?</code></td>
832 |   <td><code>concat</code></td>
833 | </tr>
834 | </table>
835 | 
836 | ### Concurrency
837 | 
838 | <table>
839 | <tr>
840 |   <th>MostJS</th>
841 |   <th>RxJS</th>
842 | </tr>
843 | <tr>
844 |   <td><code>– (<a href="https://github.com/ivan-kleshnin/reactive-polyglot/wiki/race">custom</a>)</code></td>
845 |   <td><code>amb / race</code></td>
846 | </tr>
847 | </table>
848 | 
849 | ### History
850 | 
851 | <table>
852 | <tr>
853 |   <th>MostJS</th>
854 |   <th>RxJS</th>
855 | </tr>
856 | <tr>
857 |   <td colspan="2"><code>– (<a href="history.md">custom</a>)</code></td>
858 | </tr>
859 | </table>
860 | 
861 | ### Design diffs
862 | 
863 | #### RxJS
864 | 
865 | 1. Three primitives: `Observer`, `Observable`, `Subject`.
866 | 2. Observables end on error.
867 | 3. Provides API to handle errors.
868 | 3. Does not provide API to handle ending.
869 | 
870 | #### KefirJS
871 | 
872 | 1. Two primitives: `Stream` and `Property` (like XStream).
873 | 2. Observables does not end on error (by default).
874 | 3. Provides API to handle errors.
875 | 4. Provides API to handle ending.
876 | 
877 | #### MostJS
878 | 
879 | 1. One primitive: `Stream` (+ community-driven).
880 | 2. Separate packages for [subject-like](https://github.com/TylorS/most-subject) and [property-like](https://github.com/mostjs/hold) primitives.
881 | 3. Provides API to handle errors.
882 | 4. Provides API to handle ending.
883 | 
884 | #### XStream
885 | 
886 | 1. Two primitives: `Stream` and `MemoryStream` (like KefirJS).
887 | 2. Always multicast. A Stream is like an RxJS Subject.
888 | 3. Streams end on error.
889 | 
890 | #### Common
891 | 
892 | RxJS does not emit initial `scan` value as event (use `startWith` for that).
893 | 
894 | ```js
895 | Rx.Observable.interval(100).map(x => 1)
896 |   .scan(add, 0);
897 |   .subscribe(console.log); // 1--2--3--...
898 | 
899 | Most.periodic(100, 1)
900 |   .scan(add, 0);
901 |   .observe(console.log); // 0--1--2--3--...
902 | ```
903 | 
904 | ### Found docs / API quirks
905 | 
906 | #### MostJS
907 | 
908 | `startWith` vs `sampleWith` vs `continueWith` + `recoverWith` vs `skipRepeatsWith`<br/>
909 | (val vs none vs func vs stream)
910 | 
911 | `tap` is listed in "Transform" section.
912 | 
913 | #### RxJS
914 | 
915 | `startWith` is listed in "Combine" section.
916 | 
917 | `mergeAll` is listed in "Combine" section.
918 | 
919 | `distinct` is not listed in "Filtering" section.
920 | 
921 | `takeUntil` is not listed in "Filtering" section.
922 | 
923 | `just` / `return` should be deprecated in favor of `of`.
924 | 
925 | `fromArray` should be deprecated in favor of `from`.
926 | 
927 | ### Links
928 | 
929 | [bacon-vs-kefir](https://github.com/rpominov/kefir/blob/master/bacon-vs-kefir-api.md) – BaconJS vs KefirJS API comparison
930 | 
931 | [dataflows](https://github.com/ivan-kleshnin/dataflows) – web arch. dataflow comparison
932 | 
933 | [stream-conversions](https://github.com/TylorS/stream-conversions) – tool for cross-library stream conversions
934 | 
935 | ### Additional Read
936 | 
937 | https://github.com/cujojs/most/issues/171
938 | 
939 | https://twitter.com/rpominov/status/689566111734599683
940 | 
941 | https://github.com/zenparsing/es-observable/issues/66
942 | 
943 | 
944 | 


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