xstream

constructor

constructor(producer: InternalProducer<T>);

method debug

debug: {
    (): MemoryStream<T>;
    (labelOrSpy: string): MemoryStream<T>;
    (labelOrSpy: (t: T) => any): MemoryStream<T>;
};

method endWhen

endWhen: (other: Stream<any>) => MemoryStream<T>;

method map

map: <U>(project: (t: T) => U) => MemoryStream<U>;

method mapTo

mapTo: <U>(projectedValue: U) => MemoryStream<U>;

method remember

remember: () => MemoryStream<T>;

method replaceError

replaceError: (replace: (err: any) => Stream<T>) => MemoryStream<T>;

method take

take: (amount: number) => MemoryStream<T>;

constructor

constructor(producer?: InternalProducer<T>);

property combine

static combine: CombineSignature;

• Combines multiple input streams together to return a stream whose events are arrays that collect the latest events from each input stream.

  *combine* internally remembers the most recent event from each of the input streams. When any of the input streams emits an event, that event together with all the other saved events are combined into an array. That array will be emitted on the output stream. It's essentially a way of joining together the events from multiple streams.

  Marble diagram:

  --1----2-----3--------4---
  ----a-----b-----c--d------
           combine
  ----1a-2a-2b-3b-3c-3d-4d--

  true

  Parameter stream1

  A stream to combine together with other streams.

  Parameter stream2

  A stream to combine together with other streams. Multiple streams, not just two, may be given as arguments. {Stream}

property merge

static merge: MergeSignature;

• Blends multiple streams together, emitting events from all of them concurrently.

  *merge* takes multiple streams as arguments, and creates a stream that behaves like each of the argument streams, in parallel.

  Marble diagram:

  --1----2-----3--------4---
  ----a-----b----c---d------
             merge
  --1-a--2--b--3-c---d--4---

  true

  Parameter stream1

  A stream to merge together with other streams.

  Parameter stream2

  A stream to merge together with other streams. Two or more streams may be given as arguments. {Stream}

method addListener

addListener: (listener: Partial<Listener<T>>) => void;

• Adds a Listener to the Stream.

  Parameter listener

method compose

compose: <U>(operator: (stream: Stream<T>) => U) => U;

• Passes the input stream to a custom operator, to produce an output stream.

  *compose* is a handy way of using an existing function in a chained style. Instead of writing outStream = f(inStream) you can write outStream = inStream.compose(f).

  Parameter operator

  A function that takes a stream as input and returns a stream as well. {Stream}

method create

static create: <T>(producer?: Producer<T>) => Stream<T>;

• Creates a new Stream given a Producer.

  true

  Parameter producer

  An optional Producer that dictates how to start, generate events, and stop the Stream. {Stream}

method createWithMemory

static createWithMemory: <T>(producer?: Producer<T>) => MemoryStream<T>;

• Creates a new MemoryStream given a Producer.

  true

  Parameter producer

  An optional Producer that dictates how to start, generate events, and stop the Stream. {MemoryStream}

method debug

debug: {
    (): Stream<T>;
    (labelOrSpy: string): Stream<T>;
    (labelOrSpy: (t: T) => any): Stream<T>;
};

method drop

drop: (amount: number) => Stream<T>;

• Ignores the first amount many events from the input stream, and then after that starts forwarding events from the input stream to the output stream.

  Marble diagram:

  --a---b--c----d---e--
        drop(3)
  --------------d---e--

  Parameter amount

  How many events to ignore from the input stream before forwarding all events from the input stream to the output stream. {Stream}

method empty

static empty: <T = any>() => Stream<T>;

• Creates a Stream that immediately emits the "complete" notification when started, and that's it.

  Marble diagram:

  empty
  -|

  true {Stream}

method endWhen

endWhen: (other: Stream<any>) => Stream<T>;

• Uses another stream to determine when to complete the current stream.

  When the given other stream emits an event or completes, the output stream will complete. Before that happens, the output stream will behaves like the input stream.

  Marble diagram:

  ---1---2-----3--4----5----6---
    endWhen( --------a--b--| )
  ---1---2-----3--4--|

  Parameter other

  Some other stream that is used to know when should the output stream of this operator complete. {Stream}

method filter

filter: {
    <S extends T>(passes: (t: T) => t is S): Stream<S>;
    (passes: (t: T) => boolean): Stream<T>;
};

method flatten

flatten: <R>(this: Stream<Stream<R> | MemoryStream<R>>) => Stream<R>;

• Flattens a "stream of streams", handling only one nested stream at a time (no concurrency).

  If the input stream is a stream that emits streams, then this operator will return an output stream which is a flat stream: emits regular events. The flattening happens without concurrency. It works like this: when the input stream emits a nested stream, *flatten* will start imitating that nested one. However, as soon as the next nested stream is emitted on the input stream, *flatten* will forget the previous nested one it was imitating, and will start imitating the new nested one.

  Marble diagram:

  --+--------+---------------
    \        \
     \       ----1----2---3--
     --a--b----c----d--------
            flatten
  -----a--b------1----2---3--

  {Stream}

method fold

fold: <R>(accumulate: (acc: R, t: T) => R, seed: R) => MemoryStream<R>;

• "Folds" the stream onto itself.

  Combines events from the past throughout the entire execution of the input stream, allowing you to accumulate them together. It's essentially like Array.prototype.reduce. The returned stream is a MemoryStream, which means it is already remember()'d.

  The output stream starts by emitting the seed which you give as argument. Then, when an event happens on the input stream, it is combined with that seed value through the accumulate function, and the output value is emitted on the output stream. fold remembers that output value as acc ("accumulator"), and then when a new input event t happens, acc will be combined with that to produce the new acc and so forth.

  Marble diagram:

  ------1-----1--2----1----1------
    fold((acc, x) => acc + x, 3)
  3-----4-----5--7----8----9------

  Parameter accumulate

  A function of type (acc: R, t: T) => R that takes the previous accumulated value acc and the incoming event from the input stream and produces the new accumulated value.

  Parameter seed

  The initial accumulated value, of type R. {MemoryStream}

method from

static from: <T>(
    input: PromiseLike<T> | Stream<T> | Array<T> | Observable<T>
) => Stream<T>;

• Creates a stream from an Array, Promise, or an Observable.

  true

  Parameter input

  The input to make a stream from. {Stream}

method fromArray

static fromArray: <T>(array: Array<T>) => Stream<T>;

• Converts an array to a stream. The returned stream will emit synchronously all the items in the array, and then complete.

  Marble diagram:

  fromArray([1,2,3])
  123|

  true

  Parameter array

  The array to be converted as a stream. {Stream}

method fromObservable

static fromObservable: <T>(obs: { subscribe: any }) => Stream<T>;

• Converts an Observable into a Stream.

  true

  Parameter observable

  The observable to be converted as a stream. {Stream}

method fromPromise

static fromPromise: <T>(promise: PromiseLike<T>) => Stream<T>;

• Converts a promise to a stream. The returned stream will emit the resolved value of the promise, and then complete. However, if the promise is rejected, the stream will emit the corresponding error.

  Marble diagram:

  fromPromise( ----42 )
  -----------------42|

  true

  Parameter promise

  The promise to be converted as a stream. {Stream}

method imitate

imitate: (target: Stream<T>) => void;

• *imitate* changes this current Stream to emit the same events that the other given Stream does. This method returns nothing.

  This method exists to allow one thing: **circular dependency of streams**. For instance, let's imagine that for some reason you need to create a circular dependency where stream first$ depends on stream second$ which in turn depends on first$:

  <!-- skip-example -->

  import delay from 'xstream/extra/delay'
  
  var first$ = second$.map(x => x * 10).take(3);
  var second$ = first$.map(x => x + 1).startWith(1).compose(delay(100));

  However, that is invalid JavaScript, because second$ is undefined on the first line. This is how *imitate* can help solve it:

  import delay from 'xstream/extra/delay'
  
  var secondProxy$ = xs.create();
  var first$ = secondProxy$.map(x => x * 10).take(3);
  var second$ = first$.map(x => x + 1).startWith(1).compose(delay(100));
  secondProxy$.imitate(second$);

  We create secondProxy$ before the others, so it can be used in the declaration of first$. Then, after both first$ and second$ are defined, we hook secondProxy$ with second$ with imitate() to tell that they are "the same". imitate will not trigger the start of any stream, it just binds secondProxy$ and second$ together.

  The following is an example where imitate() is important in Cycle.js applications. A parent component contains some child components. A child has an action stream which is given to the parent to define its state:

  <!-- skip-example -->

  const childActionProxy$ = xs.create();
  const parent = Parent({...sources, childAction$: childActionProxy$});
  const childAction$ = parent.state$.map(s => s.child.action$).flatten();
  childActionProxy$.imitate(childAction$);

  Note, though, that **imitate() does not support MemoryStreams**. If we would attempt to imitate a MemoryStream in a circular dependency, we would either get a race condition (where the symptom would be "nothing happens") or an infinite cyclic emission of values. It's useful to think about MemoryStreams as cells in a spreadsheet. It doesn't make any sense to define a spreadsheet cell A1 with a formula that depends on B1 and cell B1 defined with a formula that depends on A1.

  If you find yourself wanting to use imitate() with a MemoryStream, you should rework your code around imitate() to use a Stream instead. Look for the stream in the circular dependency that represents an event stream, and that would be a candidate for creating a proxy Stream which then imitates the target Stream.

  Parameter target

  The other stream to imitate on the current one. Must not be a MemoryStream.

method last

last: () => Stream<T>;

• When the input stream completes, the output stream will emit the last event emitted by the input stream, and then will also complete.

  Marble diagram:

  --a---b--c--d----|
        last()
  -----------------d|

  {Stream}

method map

map: <U>(project: (t: T) => U) => Stream<U>;

• Transforms each event from the input Stream through a project function, to get a Stream that emits those transformed events.

  Marble diagram:

  --1---3--5-----7------
     map(i => i * 10)
  --10--30-50----70-----

  Parameter project

  A function of type (t: T) => U that takes event t of type T from the input Stream and produces an event of type U, to be emitted on the output Stream. {Stream}

method mapTo

mapTo: <U>(projectedValue: U) => Stream<U>;

• It's like map, but transforms each input event to always the same constant value on the output Stream.

  Marble diagram:

  --1---3--5-----7-----
        mapTo(10)
  --10--10-10----10----

  Parameter projectedValue

  A value to emit on the output Stream whenever the input Stream emits any value. {Stream}

method never

static never: <T = any>() => Stream<T>;

• Creates a Stream that does nothing when started. It never emits any event.

  Marble diagram:

           never
  -----------------------

  true {Stream}

method of

static of: <T>(...items: Array<T>) => Stream<T>;

• Creates a Stream that immediately emits the arguments that you give to *of*, then completes.

  Marble diagram:

  of(1,2,3)
  123|

  true

  Parameter a

  The first value you want to emit as an event on the stream.

  Parameter b

  The second value you want to emit as an event on the stream. One or more of these values may be given as arguments. {Stream}

method periodic

static periodic: (period: number) => Stream<number>;

• Creates a stream that periodically emits incremental numbers, every period milliseconds.

  Marble diagram:

      periodic(1000)
  ---0---1---2---3---4---...

  true

  Parameter period

  The interval in milliseconds to use as a rate of emission. {Stream}

method remember

remember: () => MemoryStream<T>;

• Returns an output stream that behaves like the input stream, but also remembers the most recent event that happens on the input stream, so that a newly added listener will immediately receive that memorised event.

  {MemoryStream}

method removeListener

removeListener: (listener: Partial<Listener<T>>) => void;

• Removes a Listener from the Stream, assuming the Listener was added to it.

  Parameter listener

method replaceError

replaceError: (replace: (err: any) => Stream<T>) => Stream<T>;

• Replaces an error with another stream.

  When (and if) an error happens on the input stream, instead of forwarding that error to the output stream, *replaceError* will call the replace function which returns the stream that the output stream will replicate. And, in case that new stream also emits an error, replace will be called again to get another stream to start replicating.

  Marble diagram:

  --1---2-----3--4-----X
    replaceError( () => --10--| )
  --1---2-----3--4--------10--|

  Parameter replace

  A function of type (err) => Stream that takes the error that occurred on the input stream or on the previous replacement stream and returns a new stream. The output stream will behave like the stream that this function returns. {Stream}

method setDebugListener

setDebugListener: (listener: Partial<Listener<T>> | null | undefined) => void;

• Adds a "debug" listener to the stream. There can only be one debug listener, that's why this is 'setDebugListener'. To remove the debug listener, just call setDebugListener(null).

  A debug listener is like any other listener. The only difference is that a debug listener is "stealthy": its presence/absence does not trigger the start/stop of the stream (or the producer inside the stream). This is useful so you can inspect what is going on without changing the behavior of the program. If you have an idle stream and you add a normal listener to it, the stream will start executing. But if you set a debug listener on an idle stream, it won't start executing (not until the first normal listener is added).

  As the name indicates, we don't recommend using this method to build app logic. In fact, in most cases the debug operator works just fine. Only use this one if you know what you're doing.

  Parameter listener

method shamefullySendComplete

shamefullySendComplete: () => void;

• Forces the Stream to emit the "completed" event to its listeners.

  As the name indicates, if you use this, you are most likely doing something The Wrong Way. Please try to understand the reactive way before using this method. Use it only when you know what you are doing.

method shamefullySendError

shamefullySendError: (error: any) => void;

• Forces the Stream to emit the given error to its listeners.

  As the name indicates, if you use this, you are most likely doing something The Wrong Way. Please try to understand the reactive way before using this method. Use it only when you know what you are doing.

  Parameter error

  The error you want to broadcast to all the listeners of this Stream.

method shamefullySendNext

shamefullySendNext: (value: T) => void;

• Forces the Stream to emit the given value to its listeners.

  As the name indicates, if you use this, you are most likely doing something The Wrong Way. Please try to understand the reactive way before using this method. Use it only when you know what you are doing.

  Parameter value

  The "next" value you want to broadcast to all listeners of this Stream.

method startWith

startWith: (initial: T) => MemoryStream<T>;

• Prepends the given initial value to the sequence of events emitted by the input stream. The returned stream is a MemoryStream, which means it is already remember()'d.

  Marble diagram:

  ---1---2-----3---
    startWith(0)
  0--1---2-----3---

  Parameter initial

  The value or event to prepend. {MemoryStream}

method subscribe

subscribe: (listener: Partial<Listener<T>>) => Subscription;

• Adds a Listener to the Stream returning a Subscription to remove that listener.

  Parameter listener

  Returns

  {Subscription}

method take

take: (amount: number) => Stream<T>;

• Lets the first amount many events from the input stream pass to the output stream, then makes the output stream complete.

  Marble diagram:

  --a---b--c----d---e--
     take(3)
  --a---b--c|

  Parameter amount

  How many events to allow from the input stream before completing the output stream. {Stream}

method throw

static throw: (error: any) => Stream<any>;

• Creates a Stream that immediately emits an "error" notification with the value you passed as the error argument when the stream starts, and that's it.

  Marble diagram:

  throw(X)
  -X

  true

  Parameter error

  The error event to emit on the created stream. {Stream}

property insArr

insArr: Array<Stream<T>>;

property type

type: string;

call signature

(): Stream<Array<any>>;

call signature

<T1>(s1: Stream<T1>): Stream<[T1]>;

call signature

<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>,
    s7: Stream<T7>,
    s8: Stream<T8>,
    s9: Stream<T9>,
    s10: Stream<T10>
): Stream<[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10]>;

call signature

<T>(...stream: Array<Stream<T>>): Stream<Array<T>>;

call signature

(...stream: Array<Stream<any>>): Stream<Array<any>>;

call signature

<T1, T2>(s1: Stream<T1>, s2: Stream<T2>): Stream<[T1, T2]>;

call signature

<T1, T2, T3>(s1: Stream<T1>, s2: Stream<T2>, s3: Stream<T3>): Stream<
    [T1, T2, T3]
>;

call signature

<T1, T2, T3, T4>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>
): Stream<[T1, T2, T3, T4]>;

call signature

<T1, T2, T3, T4, T5>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>
): Stream<[T1, T2, T3, T4, T5]>;

call signature

<T1, T2, T3, T4, T5, T6>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>
): Stream<[T1, T2, T3, T4, T5, T6]>;

call signature

<T1, T2, T3, T4, T5, T6, T7>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>,
    s7: Stream<T7>
): Stream<[T1, T2, T3, T4, T5, T6, T7]>;

call signature

<T1, T2, T3, T4, T5, T6, T7, T8>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>,
    s7: Stream<T7>,
    s8: Stream<T8>
): Stream<[T1, T2, T3, T4, T5, T6, T7, T8]>;

call signature

<T1, T2, T3, T4, T5, T6, T7, T8, T9>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>,
    s7: Stream<T7>,
    s8: Stream<T8>,
    s9: Stream<T9>
): Stream<[T1, T2, T3, T4, T5, T6, T7, T8, T9]>;

property complete

complete: () => void;

property error

error: (err: any) => void;

property next

next: (x: T) => void;

call signature

(): Stream<any>;

call signature

<T1>(s1: Stream<T1>): Stream<T1>;

call signature

<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>,
    s7: Stream<T7>,
    s8: Stream<T8>,
    s9: Stream<T9>,
    s10: Stream<T10>
): Stream<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10>;

call signature

<T>(...stream: Array<Stream<T>>): Stream<T>;

call signature

<T1, T2>(s1: Stream<T1>, s2: Stream<T2>): Stream<T1 | T2>;

call signature

<T1, T2, T3>(s1: Stream<T1>, s2: Stream<T2>, s3: Stream<T3>): Stream<
    T1 | T2 | T3
>;

call signature

<T1, T2, T3, T4>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>
): Stream<T1 | T2 | T3 | T4>;

call signature

<T1, T2, T3, T4, T5>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>
): Stream<T1 | T2 | T3 | T4 | T5>;

call signature

<T1, T2, T3, T4, T5, T6>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>
): Stream<T1 | T2 | T3 | T4 | T5 | T6>;

call signature

<T1, T2, T3, T4, T5, T6, T7>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>,
    s7: Stream<T7>
): Stream<T1 | T2 | T3 | T4 | T5 | T6 | T7>;

call signature

<T1, T2, T3, T4, T5, T6, T7, T8>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>,
    s7: Stream<T7>,
    s8: Stream<T8>
): Stream<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8>;

call signature

<T1, T2, T3, T4, T5, T6, T7, T8, T9>(
    s1: Stream<T1>,
    s2: Stream<T2>,
    s3: Stream<T3>,
    s4: Stream<T4>,
    s5: Stream<T5>,
    s6: Stream<T6>,
    s7: Stream<T7>,
    s8: Stream<T8>,
    s9: Stream<T9>
): Stream<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9>;

method subscribe

subscribe: (listener: Listener<T>) => Subscription;

property ins

ins: Stream<T>;

property type

type: string;

property out

out: Stream<T>;

property start

start: (listener: Listener<T>) => void;

property stop

stop: () => void;

method unsubscribe

unsubscribe: () => void;