interface AsyncStream<T>

A possibly infinite asynchronous sequence of elements of type T. See the Stream documentation and the AsyncStream API documentation

Companion namespace: AsyncStream

Type parameters

Name	Description
T	the element type

example

const s1 = AsyncStream.empty<number>()
const s2 = AsyncStream.of(1, 3, 2)
const s3 = AsyncStream.from(Stream.range({ start: 10, amount: 15 }))

Methods

append

Returns the current stream succeeded by the given value

Definition

append(value: AsyncOptLazy<T>): AsyncStream.NonEmpty<T>;

Parameters

Name	Type	Description
value	AsyncOptLazy<T>	the value to append

example

await AsyncStream.of(1, 2, 3).append(4).toArray()
// => [1, 2, 3, 4]

note

O(1)

assumeNonEmpty

Returns the stream as a non-empty instance.

Definition

assumeNonEmpty(): AsyncStream.NonEmpty<T>;

throws

RimbuError.EmptyCollectionAssumedNonEmptyError if the stream is known to be empty.

example

AsyncStream.from(Stream.range({ amount: 100 })).assumeNonEmpty()
// => type: AsyncStream.NonEmpty<number>

note

the function does not actually check if the stream is empty, so treat with extra care @note O(1)

asyncStream

Returns an async stream of elements of type T.

Definition

asyncStream(): this;

example

AsyncStream.of(1, 2, 3).asyncStream()
// => returns itself

collect

Returns an AsyncStream containing the resulting elements from applying the given collectFun to each element in this Stream.

Definition

collect<R>(collectFun: AsyncCollectFun<T, R>): AsyncStream<R>;

Type parameters

Name	Description
R	the resulting element type

Parameters

Name	Type	Description
collectFun	AsyncCollectFun<T, R>	a potentially asynchronous function taking the parameters below and returning a new element or a skip token - value: the next element - index: the element index - skip: an element that can be returned if the current element should be skipped - halt: a function that, if called, ensures that no new elements are passed

example

await AsyncStream.of(1, 2, 3).collect(async (v, i, skip, halt) => {
if (i === 0) return skip;
if (i === 1) halt();
return String(v)
}).toArray();
// => ['1']

note

O(1)

concat

Returns an AsyncStream containing the elements of this stream followed by all elements produced by the others array of AsyncStreamSources.

Definitions

concat<T2 = T>(...others: ArrayNonEmpty<AsyncStreamSource.NonEmpty<T2>>): AsyncStream.NonEmpty<T | T2>;

concat<T2 = T>(...others: ArrayNonEmpty<AsyncStreamSource<T2>>): AsyncStream<T | T2>;

Type parameters

Name	Default	Description
T2	T	the element type of the stream to concatenate

Parameters

Name	Type	Description
others	ArrayNonEmpty<AsyncStreamSource.NonEmpty<T2>>	a series of AsyncStreamSources to concatenate.

example

await AsyncStream.of(1, 2, 3).concat([4, 5], () => [6, 7]).toArray()
// [1, 2, 3, 4, 5, 6, 7]

note

O(1)

contains

Returns true if the AsyncStream contains given amount instances of given value, using given eq function.

Definition

contains(value: T, options?: {
    amount?: number | undefined;
    eq?: Eq<T> | undefined;
    negate?: boolean | undefined;
  }): Promise<boolean>;

Parameters

Name	Type	Description
value	T	the value to search for
options	{     amount?: number | undefined;     eq?: Eq<T> | undefined;     negate?: boolean | undefined;   }	(optional) object specifying the following properties = amount: (default: 1) the amount of values the Stream should contain - eq: (default: Eq.objectIs) the Eq instance to use to test equality of elements - negate: (default: false) when true will negate the given predicate

example

const source = Stream.from('marmot')
await source.contains('m')    // => true
await source.contains('m', 2) // => true
await source.contains('m', 3) // => false
await source.contains('q')    // => false

note

O(N)

containsSlice

Returns true if this stream contains the same sequence of elements as the given source, false otherwise.

Definition

containsSlice(source: AsyncStreamSource.NonEmpty<T>, options?: {
    eq?: Eq<T> | undefined;
    amount?: number | undefined;
  }): Promise<boolean>;

Parameters

Name	Type	Description
source	AsyncStreamSource.NonEmpty<T>	a non-empty async stream source containing the element sequence to find
options	{     eq?: Eq<T> | undefined;     amount?: number | undefined;   }	(optional) object specifying the following properties - eq: (default: Eq.objectIs) the function to use to test element equality - negate: (default: false) when true will negate the given Eq function

example

await AsyncStream.of(1, 2, 3, 4, 5).containsSlice([2, 3, 4])
// => true
await AsyncStream.of(1, 2, 3, 4, 5).containsSlice([4, 3, 2])
// => false

count

Returns the amount of elements in the AsyncStream.

Definition

count(): Promise<number>;

example

await AsyncStream.of(1, 2, 3).count() // => 3

note

O(N) for most types of Stream @note be careful not to use on infinite streams

countElement

Returns the amount of elements that are equal according to the given eq to the given value in the AsyncStream.

Definition

countElement(value: T, options?: {
    eq?: Eq<T> | undefined;
    negate?: boolean | undefined;
  }): Promise<number>;

Parameters

Name	Type	Description
value	T	the value to compare to
options	{     eq?: Eq<T> | undefined;     negate?: boolean | undefined;   }	(optional) object specifying the following properties - eq: (default: Eq.objectIs) the Eq instance to use to test equality of elements - negate: (default: false) when true will negate the given Eq function

example

await AsyncStream.of(1, 2, 3).countElement(2) // => 1
await AsyncStream.of(1, 2, 3).countElement(2, { negate: true }) // => 2

note

O(N) @note be careful not to use on infinite streams

distinctPrevious

Returns an AsyncStream containing non-repetitive elements of the source stream, where repetitive elements are compared using the optionally given eq equality function.

Definition

distinctPrevious(options?: {
    eq?: Eq<T> | undefined;
    negate?: boolean | undefined;
  }): AsyncStream<T>;

Parameters

Name	Type	Description
options	{     eq?: Eq<T> | undefined;     negate?: boolean | undefined;   }	(optional) object specifying the following properties - eq: (default: Eq.objectIs) the Eq instance to use to test equality of elements - negate: (default: false) when true will negate the given predicate

example

await AsyncStream.of(1, 1, 2, 2, 3, 1).distinctPrevious().toArray()
// => [1, 2, 3, 1]

drop

Returns an AsyncStream that skips the first amount elements of this stream and returns the rest.

Definition

drop(amount: number): AsyncStream<T>;

Parameters

Name	Type	Description
amount	number	the amount of elements to skip

example

await AsyncStream.of(1, 2, 3).drop(1).toArray()   // => [2, 3]

note

O(N)

dropWhile

Returns an AsyncStream that contains the elements of this stream starting from the first element that does not satisfy given pred function.

Definition

dropWhile(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    negate?: boolean | undefined;
  }): AsyncStream<T>;

Parameters

Name	Type	Description
pred	(value: T, index: number) => MaybePromise<boolean>	a potentially asynchronous predicate function taking an element and its index
options	{     negate?: boolean | undefined;   }	(optional) object specifying the following properties - negate: (default: false) when true will negate the given predicate

example

await AsyncStream.of(1, 2, 3).dropWhile(async v => v < 2).toArray()
// => [2, 3]

note

O(N)

elementAt

Returns the element in the AsyncStream at the given index, or a fallback value (default undefined) otherwise.

Definitions

elementAt(index: number): Promise<T | undefined>;

elementAt<O>(index: number, otherwise: AsyncOptLazy<O>): Promise<T | O>;

Parameters

Name	Type	Description
index	number	the index of the element to retrieve

example

await AsyncStream.of(1, 2, 3).elementAt(1)        // => 2
await AsyncStream.of(1, 2, 3).elementAt(5)        // => undefined
await AsyncStream.of(1, 2, 3).elementAt(5, 'a')   // => 'a'
await AsyncStream.of(1, 2, 3).elementAt(5, async () => 'a')   // => 'a'

note

O(N) for most types of Stream

equals

Returns true if the sequence of elements in this stream are equal to the sequence in the other stream according to the provided eq function.

Definition

equals(other: AsyncStreamSource<T>, options?: {
    eq?: Eq<T> | undefined;
    negate?: boolean | undefined;
  }): Promise<boolean>;

Parameters

Name	Type	Description
other	AsyncStreamSource<T>	the other async stream to compare
options	{     eq?: Eq<T> | undefined;     negate?: boolean | undefined;   }	(optional) object specifying the following properties - eq: (default: Eq.objectIs) the Eq instance to use to test equality of elements - negate: (default: false) when true will negate the eq function

example

await AsyncStream.of(1, 2, 3).equals([1, 2, 3])     // => true
await AsyncStream.of(1, 2, 3, 4).equals([1, 2, 3])  // => false

note

don't use on potentially infinite streams @note O(N)

every

Returns true if every element of the AsyncStream satifies given pred function.

Definition

every(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    negate?: boolean | undefined;
  }): Promise<boolean>;

Parameters

Name	Type	Description
pred	(value: T, index: number) => MaybePromise<boolean>	a potentially asynchronous predicate function taking an element and its index
options	{     negate?: boolean | undefined;   }	(optional) object specifying the following properties - negate: (default: false) when true will negate the given predicate

example

await AsyncStream.of(1, 2, 3).every((v, i) => v + i > 10)  // => false
await AsyncStream.of(1, 2, 3).every(async (v, i) => v + i < 10)  // => true

note

O(N)

filter

Returns an AsyncStream containing only those elements from this stream for which the given pred function returns true.

Definitions

filter<TF extends T>(pred: (value: T, index: number, halt: () => void) => value is TF, options?: {
    negate?: false | undefined;
  }): AsyncStream<TF>;

filter<TF extends T>(pred: (value: T, index: number, halt: () => void) => value is TF, options: {
    negate: true;
  }): AsyncStream<Exclude<T, TF>>;

filter(pred: (value: T, index: number, halt: () => void) => MaybePromise<boolean>, options?: {
    negate?: boolean | undefined;
  }): AsyncStream<T>;

Type parameters

Name	Constraints	Description
TF	T

Parameters

Name	Type	Description
pred	(value: T, index: number, halt: () => void) => value is TF	a potentially asynchronous function taking an element and its index, and returning true if the element should be included in the resulting stream.
options	{     negate?: false | undefined;   }	(optional) object specifying the following properties - negate: (default: false) when true will negate the given predicate

note

if the predicate is a type guard, the return type is automatically inferred @note O(1)

example

await AsyncStream.of(1, 2, 3).filter(async (v, i) => v + i !== 3).toArray()
// => [1, 3]
await AsyncStream.of(1, 2, 3).filter(async (v, i) => v + i !== 3, { negate: true }).toArray()
// => [2]

filterPure

Returns an AsyncStream containing only those elements from this stream for which the given pred function returns true.

Definitions

filterPure<A extends readonly unknown[], TF extends T>(options: {
    pred: (value: T, ...args: A) => value is TF;
    negate?: false | undefined;
  }, ...args: A): AsyncStream<T>;

filterPure<A extends readonly unknown[], TF extends T>(options: {
    pred: (value: T, ...args: A) => value is TF;
    negate: true;
  }, ...args: A): AsyncStream<Exclude<T, TF>>;

filterPure<A extends readonly unknown[]>(options: {
    pred: (value: T, ...args: A) => MaybePromise<boolean>;
    negate?: boolean | undefined;
  }, ...args: A): AsyncStream<T>;

Type parameters

Name	Constraints	Description
A	readonly unknown[]	the type of the arguments to be passed to the pred function after each element
TF	T

Parameters

Name	Type	Description
options	{     pred: (value: T, ...args: A) => value is TF;     negate?: false | undefined;   }	object specifying the following properties - pred: a potentially asynchronous function taking an element the optionaly given args, and returning true if the element should be included in the resulting stream. - negate: (default: false) when true will negate the given predicate
args	A	(optional) the extra arguments to pass to the given mapFun

note

if the predicate is a type guard, the return type is automatically inferred @note O(1)

example

await AsyncStream.of(1, 2, 3).filterPure({ pred: Object.is }, 2).toArray()
// => [2]
await AsyncStream.of(1, 2, 3).filterPure({ pred: Object.is, negate: true }, 2).toArray()
// => [1, 3]

find

Returns the first element for which the given pred function returns true, or a fallback value otherwise.

Definitions

find<O, TF extends T>(pred: (value: T, index: number) => value is TF, options?: {
    occurrance?: number | undefined;
    negate?: false | undefined;
    otherwise: AsyncOptLazy<O>;
  }): Promise<TF | O>;

find<O, TF extends T>(pred: (value: T, index: number) => value is TF, options: {
    occurrance?: number | undefined;
    negate: true;
    otherwise: AsyncOptLazy<O>;
  }): Promise<Exclude<T, TF> | O>;

find<TF extends T>(pred: (value: T, index: number) => value is TF, options?: {
    occurrance?: number | undefined;
    negate?: false | undefined;
    otherwise?: undefined;
  }): Promise<T | undefined>;

find<TF extends T>(pred: (value: T, index: number) => value is TF, options: {
    occurrance?: number | undefined;
    negate: true;
    otherwise?: undefined;
  }): Promise<Exclude<T, TF> | undefined>;

find<O>(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    occurrance?: number | undefined;
    negate?: boolean | undefined;
    otherwise: AsyncOptLazy<O>;
  }): Promise<T | O>;

find(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    occurrance?: number | undefined;
    negate?: boolean | undefined;
    otherwise?: undefined;
  }): Promise<T | undefined>;

Type parameters

Name	Constraints	Description
O		the optional value type to return no value was found
TF	T

Parameters

Name	Type	Description
pred	(value: T, index: number) => value is TF	a potentially asynchronous predicate function taking an element and its index
options	{     occurrance?: number | undefined;     negate?: false | undefined;     otherwise: AsyncOptLazy<O>;   }	(optional) object specifying the following properties - occurrance: (default: 1) the occurrance number to look for - otherwise: (default: undefined) an OptLazy value to be returned if the Stream is empty

note

if the predicate is a type guard, the return type is automatically inferred

example

const isEven = async (v: number) => v % 2 === 0
await AsyncStream.of(1, 2, 3, 4).find(isEven)           // => 2
await AsyncStream.of(1, 2, 3, 4).find(isEven, { occurrance: 2 })        // => 4
await AsyncStream.of(1, 2, 3, 4).find(isEven, { occurrance: 3 })        // => undefined
await AsyncStream.of(1, 2, 3, 4).find(isEven, { occurrance: 3, otherwise: 'a' })
// => 'a'

note

O(N)

first

Returns the first element of the AsyncStream, or a fallback value (default undefined) if the stream is empty.

Definitions

first(): Promise<T | undefined>;

first<O>(otherwise: AsyncOptLazy<O>): Promise<T | O>;

example

await AsyncStream.of(1, 2, 3).first()      // => 1
await AsyncStream.empty<number>().first()  // => undefined
await AsyncStream.empty<number>().first(0) // => 0
await AsyncStream.empty<number>().first(async () => 0) // => 0

note

O(1)

flatMap

Returns an AsyncStream consisting of the concatenation of flatMapFun applied to each element.

Definition

flatMap<T2>(flatMapFun: (value: T, index: number, halt: () => void) => AsyncStreamSource<T2>): AsyncStream<T2>;

Type parameters

Name	Description
T2	the resulting element type

Parameters

Name	Type	Description
flatMapFun	(value: T, index: number, halt: () => void) => AsyncStreamSource<T2>	a potentially asynchronous function receiving the inputs described below and returning a StreamSource of new elements - value: the next element - index: the index of the element - halt: a function that, if called, ensures that no new elements are passed

note

O(1)

example

await AsyncStream.of(1, 2, 3).flatMap(async (v, i, halt) => {
if (i >= 1) halt();
return [v, i, v + i]
}).toArray()
// => [1, 0, 1, 2, 1, 3]

flatZip

Returns an AsyncStream consisting of the concatenation of flatMapFun applied to each element, zipped with the element that was provided to the function.

Definition

flatZip<T2>(flatMapFun: (value: T, index: number, halt: () => void) => AsyncStreamSource<T2>): AsyncStream<[T, T2]>;

Type parameters

Name	Description
T2	the result element type

Parameters

Name	Type	Description
flatMapFun	(value: T, index: number, halt: () => void) => AsyncStreamSource<T2>	a function receiving the inputs described below and returning an AsyncStreamSource of new elements - value: the next element - index: the index of the element - halt: a function that, if called, ensures that no new elements are passed

note

O(1)

example

await AsyncStream.of(1, 2, 3).flatZip((v, i, halt) => {
if (i >= 1) halt();
return [v, i, v + i]
}).toArray()
// => [[1, 1], [1, 0], [1, 1], [2, 2], [2, 1], [2, 3]]

fold

Returns the value resulting from applying the given the given next function to a current state (initially the given init value), and the next stream value, and returning the new state. When all elements are processed, the resulting state is returned.

Definition

fold<R>(init: AsyncOptLazy<R>, next: (current: R, value: T, index: number, halt: () => void) => MaybePromise<R>): Promise<R>;

Type parameters

Name	Description
R	the resulting type

Parameters

Name	Type	Description
init	AsyncOptLazy<R>	the initial result/state value
next	(current: R, value: T, index: number, halt: () => void) => MaybePromise<R>	a potentially asynchronous function taking the parameters below and returning the new result/state value - current: the current result/state value, initially init. - value: the next Stream value - index: the index of the given value - halt: a function that, if called, ensures that no new elements are passed

example

console.log(await AsyncStream.empty<number>().fold(5, async (current, value) => current + value))
// => 5
console.log(await AsyncStream.of(1, 2, 3).fold(() => 5, (current, value) => current + value))
// => 11  (= 5 + 1 + 2 + 3)

foldStream

Returns an AsyncStream containing the values resulting from applying the given the given next function to a current state (initially the given init value), and the next stream value, and returning the new state.

Definition

foldStream<R>(init: AsyncOptLazy<R>, next: (current: R, value: T, index: number, halt: () => void) => MaybePromise<R>): AsyncStream<R>;

Type parameters

Name	Description
R	the resulting element type

Parameters

Name	Type	Description
init	AsyncOptLazy<R>	the initial result/state value
next	(current: R, value: T, index: number, halt: () => void) => MaybePromise<R>	a function taking the parameters below and returning the new result/state value - current: the current result/state value, initially init. - value: the next Stream value - index: the index of the given value - halt: a function that, if called, ensures that no new elements are passed

example

console.log(
await AsyncStream.empty<number>()
.foldStream(5, async (current, value) => current + value)
.toArray()
)
// => []
console.log(
await AsyncStream.of(1, 2, 3)
.foldStream(() => 5, (current, value) => current + value)
.toArray()
)
// => [6, 8, 11]

forEach

Performs given function f for each element of the Stream, using given state as initial traversal state.

Definition

forEach(f: (value: T, index: number, halt: () => void) => MaybePromise<void>, options?: {
    state?: TraverseState | undefined;
  }): Promise<void>;

Parameters

Name	Type	Description
f	(value: T, index: number, halt: () => void) => MaybePromise<void>	the potentially asynchronous function to perform for each element, receiving: - value: the next element - index: the index of the element - halt: a function that, if called, ensures that no new elements are passed
options	{     state?: TraverseState | undefined;   }	(optional) object specifying the following properties - state: (optional) the traverse state

note

if f is an async function, each call will be awaited consecutively

example

await AsyncStream.of(1, 2, 3).forEach(async (v, i, halt) => {
console.log(v);
if (i >= 1) halt();
})
// => 1, 2

note

O(N)

forEachPure

Performs given function f for each element of the Stream, with the optionally given args as extra arguments.

Definition

forEachPure<A extends readonly unknown[]>(f: (value: T, ...args: A) => MaybePromise<void>, ...args: A): Promise<void>;

Type parameters

Name	Constraints	Description
A	readonly unknown[]	the type of the extra arguments to pass

Parameters

Name	Type	Description
f	(value: T, ...args: A) => MaybePromise<void>	the potentially asynchronous function to perform for each element, optionally receiving given extra args.
args	A	a list of extra arguments to pass to given f for each element when needed

note

if f is an async function, each call will be awaited consecutively

example

await AsyncStream.of(1, 2, 3).forEachPure(console.log, 'sheep')
// => logs:
// 1 sheep
// 2 sheep
// 3 sheep

note

O(N)

groupBy

Returns a promise resolving to the result of applying the valueToKey function to calculate a key for each value, and feeding the tuple of the key and the value to the collector reducer, and finally returning its result. If no collector is given, the default collector will return a JS multimap of the type Map<K, V[]>.

Definitions

groupBy<K, R, T2 extends readonly [K, T] = [K, T]>(valueToKey: (value: T, index: number) => MaybePromise<K>, options: {
    collector: AsyncReducer.Accept<[K, T] | T2, R>;
  }): Promise<R>;

groupBy<K>(valueToKey: (value: T, index: number) => MaybePromise<K>, options?: {
    collector?: undefined;
  }): Promise<Map<K, T[]>>;

Type parameters

Name	Constraints	Default	Description
K			the key type
R			the collector output type
T2	readonly [K, T]	[K, T]

Parameters

Name	Type	Description
valueToKey	(value: T, index: number) => MaybePromise<K>	potentially async function taking a value and its index, and returning the corresponding key
options	{     collector: AsyncReducer.Accept<[K, T] | T2, R>;   }	(optional) an object containing the following properties: - collector: (default: Reducer.toArray()) a reducer that collects the incoming tuple of key and value, and provides the output

example

await AsyncStream.of(1, 2, 3).groupBy((v) => v % 2)
// => Map {0 => [2], 1 => [1, 3]}

indexed

Returns an AsyncStream where each element in this stream is paired with its index

Definition

indexed(options?: {
    startIndex?: number | undefined;
  }): AsyncStream<[number, T]>;

Parameters

Name	Type	Description
options	{     startIndex?: number | undefined;   }	(optional) object specifying the following properties - startIndex: (optional) an alternative start index to use

example

await AsyncStream.of(1, 2, 3).indexed().toArray()
// => [[0, 1], [1, 2], [2, 3]]

note

O(1)

indexOf

Returns the index of the occurrance instance of given searchValue in the AsyncStream, using given eq function, or undefined if no such value is found.

Definition

indexOf(searchValue: T, options?: {
    occurrance?: number | undefined;
    eq?: Eq<T> | undefined;
    negate?: boolean | undefined;
  }): Promise<number | undefined>;

Parameters

Name	Type	Description
searchValue	T	the element to search for
options	{     occurrance?: number | undefined;     eq?: Eq<T> | undefined;     negate?: boolean | undefined;   }	(optional) object specifying the following properties - occurrance - (default: 1) the occurrance to search for - eq: (default: Eq.objectIs) the Eq instance to use to test equality of elements - negate: (default: false) when true will negate the given Eq function

example

const source = AsyncStream.from('marmot')
await source.indexOf('m')     // => 0
await source.indexOf('m', { occurrance: 2 })  // => 3
await source.indexOf('m', { occurrance: 3 })  // => undefined
await source.indexOf('q')     // => undefined

note

O(N)

indexWhere

Returns the index of the given occurrance instance of the element in the AsyncStream that satisfies given pred function, or undefined if no such instance is found.

Definition

indexWhere(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    occurrance?: number | undefined;
    negate?: boolean | undefined;
  }): Promise<number | undefined>;

Parameters

Name	Type	Description
pred	(value: T, index: number) => MaybePromise<boolean>	a potentially asynchronous predicate function taking an element and its index
options	{     occurrance?: number | undefined;     negate?: boolean | undefined;   }	(optional) object specifying the following properties - occurrance: (default: 1) the occurrance to search for - negate: (default: false) when true will negate the given predicate

example

await AsyncStream.of(1, 2, 3).indexWhere((v, i) => v + i > 2)      // => 1
await AsyncStream.of(1, 2, 3).indexWhere(async (v, i) => v + i > 2, { occurrance: 2 })   // => 2

note

O(N)

indicesOf

Returns an AsyncStream containing the indicies of the occurrance of the given searchValue, according to given eq function.

Definition

indicesOf(searchValue: T, options?: {
    eq?: Eq<T> | undefined;
    negate?: boolean | undefined;
  }): AsyncStream<number>;

Parameters

Name	Type	Description
searchValue	T	the value to search for
options	{     eq?: Eq<T> | undefined;     negate?: boolean | undefined;   }	(optional) object specifying the following properties - eq: (default: Eq.objectIs) the Eq instance to use to test equality of elements - negate: (default: false) when true will negate the given Eq function

example

await AsyncStream.from('marmot').indicesOf('m').toArray()
// => [0, 3]

note

O(N)

indicesWhere

Returns an AsyncStream containing the indices of the elements for which the given pred function returns true.

Definition

indicesWhere(pred: (value: T) => MaybePromise<boolean>, options?: {
    negate?: boolean | undefined;
  }): AsyncStream<number>;

Parameters

Name	Type	Description
pred	(value: T) => MaybePromise<boolean>	a potentially asynchronous predicate function taking an element
options	{     negate?: boolean | undefined;   }	(optional) object specifying the following properties - negate: (default: false) when true will negate the given predicate

example

await AsyncStream.of(1, 2, 3).indicesWhere((v, i) => v + i !== 3).toArray()
// => [0, 2]

note

O(N)

intersperse

Returns an AsyncStream with all elements from the given sep AsyncStreamSource between two elements of this stream.

Definition

intersperse(sep: AsyncStreamSource<T>): AsyncStream<T>;

Parameters

Name	Type	Description
sep	AsyncStreamSource<T>	the AsyncStreamSource to insert between each element of this Stream

example

await AsyncStream.of(1, 2, 3).intersperse("ab").toArray()
// => [1, 'a', 'b', 2, 'a', 'b', 3]

note

O(1)

join

Returns a string resulting from converting each element to string with options.valueToString, interspersed with options.sep, starting with options.start and ending with options.end.

Definition

join(options?: {
    sep?: string | undefined;
    start?: string | undefined;
    end?: string | undefined;
    valueToString?: ((value: T) => MaybePromise<string>) | undefined;
    ifEmpty?: string | undefined;
  }): Promise<string>;

Parameters

Name	Type	Description
options	{     sep?: string | undefined;     start?: string | undefined;     end?: string | undefined;     valueToString?: ((value: T) => MaybePromise<string>) | undefined;     ifEmpty?: string | undefined;   }	(optional) object specifying the following properties - sep: (optional) a seperator to insert between each Stream element - start: (optional) a start string to prepend at the start - end: (optional) an end string to append at the end - valueToString: (default: String) a potentially asynchronous function converting a Stream element to a string - ifEmpty: (optional) a string to return instead of the start and end tag if the stream is empty

example

await AsyncStream.of(1, 2, 3).join({ start: '<', sep: ', ', end: '>' })
// => '<1, 2, 3>'

note

O(N)

last

Returns the last element of the AsyncStream, or a fallback value (default undefined) if the stream is empty.

Definitions

last(): Promise<T | undefined>;

last<O>(otherwise: AsyncOptLazy<O>): Promise<T | O>;

example

await AsyncStream.of(1, 2, 3).last()      // => 3
await AsyncStream.empty<number>().last()  // => undefined
await AsyncStream.empty<number>().last(0) // => 0
await AsyncStream.empty<number>().last(async () => 0) // => 0

note

O(N)

map

Returns an AsyncStream where mapFun is applied to each element.

Definition

map<T2>(mapFun: (value: T, index: number) => MaybePromise<T2>): AsyncStream<T2>;

Type parameters

Name	Description
T2	the resulting element type

Parameters

Name	Type	Description
mapFun	(value: T, index: number) => MaybePromise<T2>	a potentially asynchronous function taking an element and its index, and returning some new element

example

await AsyncStream.of(1, 2, 3).map(async (v, i) => `[${i}]: ${v}`).toArray()
// => ['[0]: 1', '[1]: 2', '[2]: 3']

note

O(1)

mapPure

Returns an AsyncStream where the given mapFun is applied to each value in the stream, with optionally as extra arguments the given args.

Definition

mapPure<T2, A extends readonly unknown[]>(mapFun: (value: T, ...args: A) => MaybePromise<T2>, ...args: A): AsyncStream<T2>;

Type parameters

Name	Constraints	Description
T2		the result value type
A	readonly unknown[]	the type of arguments to be supplied to the mapFun after each element

Parameters

Name	Type	Description
mapFun	(value: T, ...args: A) => MaybePromise<T2>	a potentially asynchronous function taking an element and the given args, and returning the resulting stream value
args	A	(optional) the extra arguments to pass to the given mapFun when needed

note

is mostly aimed to increase performance so that an extra function is not required @note can be used on function that really expect 1 argument, since the normal map will also pass more arguments

example

const s = AsyncStream.of({ a: 1 }, { a: 2, c: { d: true } })
const s2 = s.mapPure(JSON.stringify, ['a'], 5)
// when stream is evaluated, will call JSON.stringify on each stream element with the given extra arguments
console.log(await s2.toArray())
// => ["{\n \"a\": 1\n}", "{\n \"a\": 2\n}"]

max

Returns the maximum element of the AsyncStream according to a default compare function, or the provided otherwise fallback value if the stream is empty.

Definitions

max(): Promise<T | undefined>;

max<O>(otherwise: AsyncOptLazy<O>): Promise<T | O>;

example

await AsyncStream.of(5, 1, 3).max()         // => 5
await AsyncStream.empty<number>().max()     // => undefined
await AsyncStream.empty<number>().max('a')  // => 'a'

note

O(N)

maxBy

Returns the maximum element of the AsyncStream according to the provided compare function, or the provided otherwise fallback value if the stream is empty.

Definitions

maxBy(compare: (v1: T, v2: T) => number): Promise<T | undefined>;

maxBy<O>(compare: (v1: T, v2: T) => number, otherwise: AsyncOptLazy<O>): Promise<T | O>;

Parameters

Name	Type	Description
compare	(v1: T, v2: T) => number

example

function compareLength(a: string, b: string): number { return b.length - a.length };
await AsyncStream.of('abc', 'a', 'ab').maxBy(compareLength)   // => 'abc'
await AsyncStream.empty<string>().maxBy(compareLength)        // => undefined
await AsyncStream.empty<string>().maxBy(compareLength, 'a')   // => 'a'

note

O(N)

min

Returns the mimimum element of the AsyncStream according to a default compare function, or the provided otherwise fallback value if the stream is empty.

Definitions

min(): Promise<T | undefined>;

min<O>(otherwise: AsyncOptLazy<O>): Promise<T | O>;

example

await AsyncStream.of(5, 1, 3).min()         // => 1
await AsyncStream.empty<number>().min()     // => undefined
await AsyncStream.empty<number>().min('a')  // => 'a'
await AsyncStream.empty<number>().min(async () => 'a')  // => 'a'

note

O(N)

minBy

Returns the mimimum element of the AsyncStream according to the provided compare function, or the provided otherwise fallback value if the stream is empty.

Definitions

minBy(compare: (v1: T, v2: T) => number): Promise<T | undefined>;

minBy<O>(compare: (v1: T, v2: T) => number, otherwise: AsyncOptLazy<O>): Promise<T | O>;

Parameters

Name	Type	Description
compare	(v1: T, v2: T) => number

example

function compareLength(a: string, b: string): number { return b.length - a.length };
await AsyncStream.of('abc', 'a', 'ab').minBy(compareLength)   // => 'a'
await AsyncStream.empty<string>().minBy(compareLength)        // => undefined
await AsyncStream.empty<string>().minBy(compareLength, 'a')   // => 'a'

note

O(N)

mkGroup

Returns an AsyncStream starting with options.sep, then returning the elements of this Stream interspersed with options.sep, and ending with options.end.

Definition

mkGroup(options: {
    sep?: AsyncStreamSource<T> | undefined;
    start?: AsyncStreamSource<T> | undefined;
    end?: AsyncStreamSource<T> | undefined;
  }): AsyncStream<T>;

Parameters

Name	Type	Description
options	{     sep?: AsyncStreamSource<T> | undefined;     start?: AsyncStreamSource<T> | undefined;     end?: AsyncStreamSource<T> | undefined;   }	object specifying the following properties - sep: (optional) a seperator StreamSource to insert between each Stream element - start: (optional) a start StreamSource to prepend - end: (optional) an end StreamSource to append

example

await AsyncStream.of(1, 2, 3).mkGroup({ start: '<<', sep: '-', end: '>>' }).toArray()
// => ['<', '<', 1, '-', 2, '-', 3, '>', '>']

note

O(N)

partition

Returns a promise resolving to a tuple of which the first element is the result of collecting the elements for which the given predicate is true, and the second one the result of collecting the other elements. Own reducers can be provided as collectors, by default the values are collected into an array.

Definitions

partition<T2 extends T, RT, RF = RT>(pred: (value: T, index: number) => value is T2, options: {
    collectorTrue: AsyncReducer.Accept<T2, RT>;
    collectorFalse: AsyncReducer.Accept<Exclude<T, T2>, RF>;
  }): Promise<[true: RT, false: RF]>;

partition<T2 extends T>(pred: (value: T, index: number) => value is T2, options?: {
    collectorTrue?: undefined;
    collectorFalse?: undefined;
  }): Promise<[true: T2[], false: Exclude<T, T2>[]]>;

partition<RT, RF = RT, T2 extends T = T>(pred: (value: T, index: number) => MaybePromise<boolean>, options: {
    collectorTrue: AsyncReducer.Accept<T | T2, RT>;
    collectorFalse: AsyncReducer.Accept<T | T2, RF>;
  }): Promise<[true: RT, false: RF]>;

partition(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    collectorTrue?: undefined;
    collectorFalse?: undefined;
  }): Promise<[true: T[], false: T[]]>;

Type parameters

Name	Constraints	Default	Description
T2	T
RT			the reducer result type for the collectorTrue value
RF		RT	the reducer result type for the collectorFalse value

Parameters

Name	Type	Description
pred	(value: T, index: number) => value is T2	a potentially async predicate receiving the value and its index
options	{     collectorTrue: AsyncReducer.Accept<T2, RT>;     collectorFalse: AsyncReducer.Accept<Exclude<T, T2>, RF>;   }	(optional) an object containing the following properties: - collectorTrue: (default: Reducer.toArray()) a reducer that collects the values for which the predicate is true - collectorFalse: (default: Reducer.toArray()) a reducer that collects the values for which the predicate is false

note

if the predicate is a type guard, the return type is automatically inferred

prepend

Returns the current stream preceded by the given value

Definition

prepend(value: AsyncOptLazy<T>): AsyncStream.NonEmpty<T>;

Parameters

Name	Type	Description
value	AsyncOptLazy<T>	the value to prepend

example

await AsyncStream.of(1, 2, 3).prepend(0).toArray()
// => [0, 1, 2, 3]

note

O(1)

reduce

Applies the given (Async)Reducer to each element in the AsyncStream, and returns the final result.

Definitions

reduce<R, T2 extends T = T>(reducer: AsyncReducer.Accept<T | T2, R>): Promise<R>;

reduce<const S extends AsyncReducer.CombineShape<T>>(shape: S & AsyncReducer.CombineShape<T>): Promise<AsyncReducer.CombineResult<S>>;

Type parameters

Name	Constraints	Default	Description
R			the resulting type
T2	T	T

Parameters

Name	Type	Description
reducer	AsyncReducer.Accept<T | T2, R>	the (Async)Reducer instance to use to apply to all stream elements.

example

console.log(await AsyncStream.of(1, 2, 4).reduce(Reducer.sum))
// => 7
console.log(await AsyncStream.of(1, 2, 4).reduce(Reducer.product))
// => 8

reduceStream

Returns an AsyncStream where the given AsyncReducer is applied to each element in the stream.

Definitions

reduceStream<R, T2 extends T = T>(reducer: AsyncReducer.Accept<T |T2, R>):AsyncStream<R>;

reduceStream<const S extends AsyncReducer.CombineShape<T>>(shape: S & AsyncReducer.CombineShape<T>): AsyncStream<AsyncReducer.CombineResult<S>>;

Type parameters

Name	Constraints	Default	Description
R			the resulting element type
T2	T	T

Parameters

Name	Type	Description
reducer	AsyncReducer.Accept<T | T2, R>	the (Async)Reducer instance to use to apply to all stream elements.

example

console.log(
await AsyncStream.of(1, 2, 4)
.reduceStream(Reducer.sum)
.toArray()
)
// => [1, 3, 7]
console.log(
await AsyncStream.of(1, 2, 4)
.reduce(Reducer.product)
.toArray()
)
// => [1, 2, 8]

repeat

Returns an AsyncStream that returns the elements from this stream given amount of times.

Definition

repeat(amount?: number |undefined):AsyncStream<T>;

Parameters

Name	Type	Description
amount	number | undefined	(default: undefined) the amount of times to return this Stream

example

const source = AsyncStream.of(1, 2, 3)
source.repeat()              // => AsyncStream(1, 2, 3, 1, 2, 3, 1, 2, ...)
await source.repeat(1).toArray()   // => [1, 2, 3]
await source.repeat(3).toArray()   // => [1, 2, 3, 1, 2, 3, 1, 2, 3]
await source.repeat(-3).toArray()  // => [1, 2, 3]

note

amount = undefined means that the AsyncStream is repeated indefintely @note amount = 1 means that the Stream is not repeated @note amount < 1 will be normalized to amount = 1 @note O(1)

single

Returns the first element of the Stream if it only has one element, or a fallback value if the Stream does not have exactly one value.

Definitions

single(): Promise<T | undefined>;

single<O>(otherwise: AsyncOptLazy<O>): Promise<T | O>;

example

await AsyncStream.empty<number>().single()  // => undefined
await AsyncStream.of(1, 2, 3).single()      // => undefined
await AsyncStream.of(1).single()            // => 1
await AsyncStream.of(1, 2, 3).single(0)     // => 0

some

Returns true if any element of the AsyncStream satifies given pred function.

Definition

some(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    negate?: boolean | undefined;
  }): Promise<boolean>;

Parameters

Name	Type	Description
pred	(value: T, index: number) => MaybePromise<boolean>	a potentially asynchonous predicate function taking an element and its index
options	{     negate?: boolean | undefined;   }	(optional) object specifying the following properties - negate: (default: false) when true will negate the given predicate

example

await AsyncStream.of(1, 2, 3).some((v, i) => v + i > 10) // => false
await AsyncStream.of(1, 2, 3).some(async (v, i) => v + i > 1)  // => true

note

O(N)

splitOn

Returns an AsyncStream of collections of stream elements, where each array is filled with elements of this stream up to the next element that equals given sepElem according to the given eq function.

Definitions

splitOn<R, T2 extends T = T>(sepElem: T, options?: {
    eq?: Eq<T> | undefined;
    negate?: boolean | undefined;
    collector: AsyncReducer.Accept<T | T2, R>;
  }): AsyncStream<R>;

splitOn(sepElem: T, options?: {
    eq?: Eq<T> | undefined;
    negate?: boolean | undefined;
    collector?: undefined;
  }): AsyncStream<T[]>;

Type parameters

Name	Constraints	Default	Description
R			the result type of the collector and the resulting stream element type
T2	T	T

Parameters

Name	Type	Description
sepElem	T	the separator element to look for
options	{     eq?: Eq<T> | undefined;     negate?: boolean | undefined;     collector: AsyncReducer.Accept<T | T2, R>;   }	(optional) object specifying the following properties - eq: (default: Eq.objectIs) the Eq instance to use to test equality of elements - negate: (default: false) when true will negate the given Eq function - collector: (default: AsyncArray.toArray()) the async reducer to use to collect the resulting values

example

await AsyncStream.from('marmot').splitOn('m').toArray()  // => [[], ['a', 'r'], ['o', 't']]

note

O(1)

splitOnSlice

Returns an AsyncStream of collections of stream elements, where each array is filled with elements of this stream up to the next sequence of elements that matches given sepSeq ordered elements with the given eq function.

Definitions

splitOnSlice<R, T2 extends T = T>(sepSlice: AsyncStreamSource<T>, options: {
    eq?: Eq<T> | undefined;
    collector: AsyncReducer.Accept<T | T2, R>;
  }): AsyncStream<R>;

splitOnSlice(sepSlice: AsyncStreamSource<T>, options?: {
    eq?: Eq<T> | undefined;
    collector?: undefined;
  }): AsyncStream<T[]>;

Type parameters

Name	Constraints	Default	Description
R			the result type of the collector and the resulting stream element type
T2	T	T

Parameters

Name	Type	Description
sepSlice	AsyncStreamSource<T>	an AsyncStreamSource contaning the sequence to find
options	{     eq?: Eq<T> | undefined;     collector: AsyncReducer.Accept<T | T2, R>;   }	(optional) object specifying the following properties - eq: (default: Eq.objectIs) the Eq instance to use to test equality of elements - collector: (default: AsyncArray.toArray()) the async reducer to use to collect the resulting values

example

await AsyncStream.from('marmalade').splitSeq('ma').toArray()  // => [[], ['r'], ['l', 'a', 'd', 'e']]

note

O(1)

splitWhere

Returns an AsyncStream of collections of stream elements, where each array is filled with elements of this stream up to the next element that satisfies give function pred.

Definitions

splitWhere<R, T2 extends T = T>(pred: (value: T, index: number) => MaybePromise<boolean>, options: {
    negate?: boolean | undefined;
    collector: AsyncReducer.Accept<T | T2, R>;
  }): AsyncStream<R>;

splitWhere(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    negate?: boolean | undefined;
    collector?: undefined;
  }): AsyncStream<T[]>;

Type parameters

Name	Constraints	Default	Description
R			the result type of the collector and the resulting stream element type
T2	T	T

Parameters

Name	Type	Description
pred	(value: T, index: number) => MaybePromise<boolean>	a potentially asynchronous predicate function taking an element and its index
options	{     negate?: boolean | undefined;     collector: AsyncReducer.Accept<T | T2, R>;   }	(optional) object specifying the following properties - negate: (default: false) when true will negate the given predicate - collector: (default: AsyncArray.toArray()) the async reducer to use to collect the resulting values

example

await AsyncStream.of(1, 2, 3, 4).splitWhere(async v => v == 3).toArray()
// => [[1, 2], [4]]

note

O(1)

take

Returns an AsyncStream that contains the elements of this stream up to a maximum of amount elements.

Definition

take(amount: number): AsyncStream<T>;

Parameters

Name	Type	Description
amount	number	the maximum amount of elements to return from the resulting Stream

example

await AsyncStream.of(1, 2, 3).take(2).toArray()   // => [1, 2]

note

O(N)

takeWhile

Returns an AsyncStream that contains the elements of this stream up to the first element that does not satisfy given pred function.

Definition

takeWhile(pred: (value: T, index: number) => MaybePromise<boolean>, options?: {
    negate?: boolean | undefined;
  }): AsyncStream<T>;

Parameters

Name	Type	Description
pred	(value: T, index: number) => MaybePromise<boolean>	a potentially asynchronous predicate function taking an element and its index
options	{     negate?: boolean | undefined;   }	(optional) object specifying the following properties - negate: (default: false) when true will negate the given predicate

example

await AsyncStream.of(1, 2, 3).takeWhile(async v => v < 3).toArray()
// => [1, 2]

note

O(N)

toArray

Returns an Array containing all elements in the AsyncStream.

Definition

toArray(): Promise<T[]>;

example

await AsyncStream.of(1, 2, 3).toArray()   // => [1, 2, 3]

toJSON

Returns a JSON representation of the AsyncStream.

Definition

toJSON(): Promise<ToJSON<T[], 'AsyncStream'>>;

note

take care not to call on infinite Streams

example

await AsyncStream.of(1, 2, 3).toJSON()   // => { dataType: 'AsyncStream', value: [1, 2, 3] }

toString

Returns a string representation of the AsyncStream.

Definition

toString(): string;

note

to avoid issues with potentially infinite stream, this method does not list the stream elements. To do this, use join.

example

AsyncStream.of(1, 2, 3).toString()   // => 'AsyncStream(...<potentially empty>)'

transform

Returns an AsyncStream consisting of the concatenation of AsyncStreamSource elements resulting from applying the given reducer to each element.

Definition

transform<R, T2 extends T = T>(transformer: AsyncTransformer.Accept<T |T2, R>):AsyncStream<R>;

Type parameters

Name	Constraints	Default	Description
R			the resulting element type
T2	T	T

Parameters

Name	Type	Description
transformer	AsyncTransformer.Accept<T | T2, R>	an async reducer taking elements ot type T as input, and returing an AsyncStreamSource of element type R

note

O(1)

example

await AsyncStream.of(1, 2, 3, 4, 5, 6).transform(AsyncTransformer.window(3)).toArray()
// => [[1, 2, 3], [4, 5, 6]]

window

Returns an AsyncStream containing windows of windowSize consecutive elements of the source stream, with each window starting skipAmount elements after the previous one.

Definitions

window<R, T2 extends T = T>(windowSize: number, options: {
    skipAmount?: number | undefined;
    collector: AsyncReducer.Accept<T | T2, R>;
  }): AsyncStream<R>;

window(windowSize: number, options?: {
    skipAmount?: number | undefined;
    collector?: undefined;
  }): AsyncStream<T[]>;

Type parameters

Name	Constraints	Default	Description
R			the collector reducer result type
T2	T	T

Parameters

Name	Type	Description
windowSize	number	the size in elements of the windows
options	{     skipAmount?: number | undefined;     collector: AsyncReducer.Accept<T | T2, R>;   }	(optional) object specifying the following properties - skipAmount: (default: windowSize) the amount of elements to skip to start the next window - collector: (default: AsyncArray.toArray()) the async reducer to use to collect the window values

example

await Stream.of(1, 2, 3, 4, 5, 6, 7).window(3).toArray()
// => [[1, 2, 3], [4, 5, 6]]
await Stream.of(1, 2, 3, 4, 5).window(3, 1).toArray()
// => [[1, 2, 3], [2, 3, 4], [3, 4, 5]]
await Stream.of(1, 2, 3, 4).window(2, 2, AsyncReducer.toJSSet()).toArray()
// => [Set(1, 2), Set(3, 4)]

withOnly

Returns an AsyncStream containing only those elements that are in the given values array.

Definition

withOnly<F extends T>(values: F[]): AsyncStream<F>;

Type parameters

Name	Constraints	Description
F	T	a subtype of T to indicate the resulting element type

Parameters

Name	Type	Description
values	F[]	an array of values to include

without

Returns an AsyncStream containing all elements except the elements in the given values array.

Definition

without<F extends T>(values: F[]): AsyncStream<T extends Exclude<T, F> ? T : Exclude<T, F>>;

Type parameters

Name	Constraints	Description
F	T	a subtype of T to indicate the resulting element type

Parameters

Name	Type	Description
values	F[]	an array of values to exclude