Type of the elements/values in the stream/property
Contains a structured version of what toString returns.
The structured description is an object that contains the fields context, method and args.
For example, for Bacon.fromArray([1,2,3]).desc you'd get
{ context: "Bacon", method: "fromArray", args: [[1,2,3]] }
Unique numeric id of this Observable. Implemented using a simple counter starting from 1.
Creates a Property that indicates whether
observable is awaiting otherObservable, i.e. has produced a value after the latest
value from otherObservable. This is handy for keeping track whether we are
currently awaiting an AJAX response:
var showAjaxIndicator = ajaxRequest.awaiting(ajaxResponse)Throttles the observable using a buffer so that at most one value event in minimumInterval is issued.
Unlike throttle, it doesn't discard the excessive events but buffers them instead, outputting
them with a rate of at most one value per minimumInterval.
Example:
var throttled = source.bufferingThrottle(2)source: asdf----asdf----
throttled: a-s-d-f-a-s-d-f-Creates a stream of changes to the Property. The stream does not include an event for the current value of the Property at the time this method was called. For EventStreams, this method returns the stream itself.
Concatenates two streams/properties into one stream/property so that
it will deliver events from this observable until it ends and then deliver
events from other. This means too that events from other,
occurring before the end of this observable will not be included in the result
stream/property.
Throttles stream/property by given amount
of milliseconds, but so that event is only emitted after the given
"quiet period". Does not affect emitting the initial value of a Property.
The difference of throttle and debounce is the same as it is in the
same methods in jQuery.
Example:
source: asdf----asdf----
source.debounce(2): -----f-------f--Passes the first event in the stream through, but after that, only passes events after a given number of milliseconds have passed since previous output.
Example:
source: asdf----asdf----
source.debounceImmediate(2): a-d-----a-d-----Decodes input using the given mapping. Is a
bit like a switch-case or the decode function in Oracle SQL. For
example, the following would map the value 1 into the string "mike"
and the value 2 into the value of the who property.
property.decode({1 : "mike", 2 : who})This is actually based on combineTemplate so you can compose static
and dynamic data quite freely, as in
property.decode({1 : { type: "mike" }, 2 : { type: "other", whoThen : who }})Delays the stream/property by given amount of milliseconds. Does not delay the initial value of a Property.
var delayed = source.delay(2)source: asdf----asdf----
delayed: --asdf----asdf--Returns the an array of dependencies that the Observable has. For instance, for a.map(function() {}).deps(), would return [a].
This method returns the "visible" dependencies only, skipping internal details. This method is thus suitable for visualization tools.
Internally, many combinator functions depend on other combinators to create intermediate Observables that the result will actually depend on.
The deps method will skip these internal dependencies. See also: internalDeps
Returns a Property that represents the result of a comparison between the previous and current value of the Observable. For the initial value of the Observable, the previous value will be the given start.
Example:
var distance = function (a,b) { return Math.abs(b - a) }
Bacon.sequentially(1, [1,2,3]).diff(0, distance)This would result to following elements in the result stream:
1 - 0 = 1 2 - 1 = 1 3 - 2 = 1
Returns a stream/property where the function f
is executed for each value, before dispatching to subscribers. This is
useful for debugging, but also for stuff like calling the
preventDefault() method for events. In fact, you can
also use a property-extractor string instead of a function, as in
".preventDefault".
Please note that for Properties, it's not guaranteed that the function will be called exactly once per event; when a Property loses all of its subscribers it will re-emit its current value when a new subscriber is added.
Logs each value of the Observable to the console. doLog() behaves like log
but does not subscribe to the event stream. You can think of doLog() as a
logger function that – unlike log() – is safe to use in production. doLog() is
safe, because it does not cause the same surprising side-effects as log()
does.
Returns a stream containing Error events only.
Same as filtering with a function that always returns false.
Filters values using given predicate function.
Instead of a function, you can use a constant value (true to include all, false to exclude all).
You can also filter values based on the value of a
property. Event will be included in output if and only if the property holds true
at the time of the event.
Takes the first element from the stream. Essentially observable.take(1).
For each element in the source stream, spawn a new
stream/property using the function f. Collect events from each of the spawned
streams into the result stream/property. Note that instead of a function, you can provide a
stream/property too. Also, the return value of function f can be either an
Observable (stream/property) or a constant value.
stream.flatMap() can be used conveniently with Bacon.once() and Bacon.never()
for converting and filtering at the same time, including only some of the results.
Example - converting strings to integers, skipping empty values:
stream.flatMap(function(text) {
return (text != "") ? parseInt(text) : Bacon.never()
})A flatMapWithConcurrencyLimit with limit of 1.
Like flatMap, but only spawns a new
stream if the previously spawned stream has ended.
Like flatMap, but instead of including events from
all spawned streams, only includes them from the latest spawned stream.
You can think this as switching from stream to stream.
Note that instead of a function, you can provide a stream/property too.
A super method of flatMap family. It limits the number of open spawned streams and buffers incoming events.
flatMapConcat is flatMapWithConcurrencyLimit(1) (only one input active),
and flatMap is flatMapWithConcurrencyLimit ∞ (all inputs are piped to output).
Groups stream events to new streams by keyF. Optional limitF can be provided to limit grouped
stream life. Stream transformed by limitF is passed on if provided. limitF gets grouped stream
and the original event causing the stream to start as parameters.
Calculator for grouped consecutive values until group is cancelled:
var events = [
{id: 1, type: "add", val: 3 },
{id: 2, type: "add", val: -1 },
{id: 1, type: "add", val: 2 },
{id: 2, type: "cancel"},
{id: 3, type: "add", val: 2 },
{id: 3, type: "cancel"},
{id: 1, type: "add", val: 1 },
{id: 1, type: "add", val: 2 },
{id: 1, type: "cancel"}
]
function keyF(event) {
return event.id
}
function limitF(groupedStream, groupStartingEvent) {
var cancel = groupedStream.filter(function(x) { return x.type === "cancel"}).take(1)
var adds = groupedStream.filter(function(x) { return x.type === "add" })
return adds.takeUntil(cancel).map(".val")
}
Bacon.sequentially(2, events)
.groupBy(keyF, limitF)
.flatMap(function(groupedStream) {
return groupedStream.fold(0, function(acc, x) { return acc + x })
})
.onValue(function(sum) {
console.log(sum)
// returns [-1, 2, 8] in an order
})Pauses and buffers the event stream if last event in valve is truthy. All buffered events are released when valve becomes falsy.
Returns the true dependencies of the observable, including the intermediate "hidden" Observables. This method is for Bacon.js internal purposes but could be useful for debugging/analysis tools as well. See also: deps
Takes the last element from the stream. None, if stream is empty.
Note:* neverEndingStream.last() creates the stream which doesn't produce any events and never ends.
Logs each value of the Observable to the console. It optionally takes arguments to pass to console.log() alongside each value. To assist with chaining, it returns the original Observable. Note that as a side-effect, the observable will have a constant listener and will not be garbage-collected. So, use this for debugging only and remove from production code. For example:
myStream.log("New event in myStream")or just
myStream.log()Maps values using given function, returning a new stream/property. Instead of a function, you can also provide a Property, in which case each element in the source stream will be mapped to the current value of the given property.
Sets the name of the observable. Overrides the default
implementation of toString and inspect.
Returns the same observable, with mutated name.
Returns a stream/property that inverts boolean values (using !)
Subscribes a given handler function to the observable. Function will be called for each new value.
This is the simplest way to assign a side-effect to an observable. The difference
to the subscribe method is that the actual stream values are
received, instead of Event objects.
Just like subscribe, this method returns a function for unsubscribing.
stream.onValue and property.onValue behave similarly, except that the latter also
pushes the initial value of the property, in case there is one.
A synonym for fold.
Creates an EventStream/Property by sampling this
stream/property value at each event from the sampler stream. The result
will contain the sampled value at each event in the source stream.
Scans stream/property with given seed value and accumulator function, resulting to a Property. For example, you might use zero as seed and a "plus" function as the accumulator to create an "integral" property. Instead of a function, you can also supply a method name such as ".concat", in which case this method is called on the accumulator value and the new stream value is used as argument.
Example:
var plus = function (a,b) { return a + b }
Bacon.sequentially(1, [1,2,3]).scan(0, plus)This would result to following elements in the result stream:
seed value = 0 0 + 1 = 1 1 + 2 = 3 3 + 3 = 6
When applied to a Property as in r = p.scan(seed, f), there's a (hopefully insignificant) catch:
The starting value for r depends on whether p has an
initial value when scan is applied. If there's no initial value, this works
identically to EventStream.scan: the seed will be the initial value of
r. However, if r already has a current/initial value x, the
seed won't be output as is. Instead, the initial value of r will be f(seed, x). This makes sense,
because there can only be 1 initial value for a Property at a time.
Skips the first n elements from the stream
Drops consecutive equal elements. So,
from [1, 2, 2, 1] you'd get [1, 2, 1]. Uses the === operator for equality
checking by default. If the isEqual argument is supplied, checks by calling
isEqual(oldValue, newValue). For instance, to do a deep comparison,you can
use the isEqual function from underscore.js
like stream.skipDuplicates(_.isEqual).
Returns a new stream/property which excludes all Error events in the source
Skips elements from the source, until a value event
appears in the given starter stream/property. In other words, starts delivering values
from the source after first value appears in starter.
Skips elements until the given predicate function returns falsy once, and then
lets all events pass through. Instead of a predicate you can also pass in a Property<boolean> to skip elements
while the Property holds a truthy value.
Returns a Property that represents a
"sliding window" into the history of the values of the Observable. The
result Property will have a value that is an array containing the last n
values of the original observable, where n is at most the value of the
max argument, and at least the value of the min argument. If the
min argument is omitted, there's no lower limit of values.
For example, if you have a stream s with value a sequence 1 - 2 - 3 - 4 - 5, the
respective values in s.slidingWindow(2) would be [] - [1] - [1,2] -
[2,3] - [3,4] - [4,5]. The values of s.slidingWindow(2,2)would be
[1,2] - [2,3] - [3,4] - [4,5].
Adds a starting value to the stream/property, i.e. concats a single-element stream containing the single seed value with this stream.
subscribes given handler function to event stream. Function will receive event objects
for all new value, end and error events in the stream.
The subscribe() call returns a unsubscribe function that you can call to unsubscribe.
You can also unsubscribe by returning Bacon.noMore from the handler function as a reply
to an Event.
stream.subscribe and property.subscribe behave similarly, except that the latter also
pushes the initial value of the property, in case there is one.
the handler function
Takes at most n values from the stream and then ends the stream. If the stream has
fewer than n values then it is unaffected.
Equal to Bacon.never() if n <= 0.
Takes elements from source until a value event appears in the other stream. If other stream ends without value, it is ignored.
Takes while given predicate function holds true, and then ends. Alternatively, you can supply a boolean Property to take elements while the Property holds true.
Throttles stream/property by given amount
of milliseconds. Events are emitted with the minimum interval of
delay. The implementation is based on stream.bufferWithTime.
Does not affect emitting the initial value of a Property.
Example:
var throttled = source.throttle(2)source: asdf----asdf----
throttled: --s--f----s--f--Returns a Promise which will be resolved with the last event coming from an Observable. The global ES6 promise implementation will be used unless a promise constructor is given. Use a shim if you need to support legacy browsers or platforms. caniuse promises.
See also firstToPromise.
In case of EventStream, creates a Property based on the EventStream.
In case of Property, returns the Property itself.
Returns a textual description of the Observable. For instance, Bacon.once(1).map(function() {}).toString() would return "Bacon.once(1).map(function)".
TODO: proper documentation missing Lets you do more custom event handling: you get all events to your function and you can output any number of events and end the stream if you choose. For example, to send an error and end the stream in case a value is below zero:
if (Bacon.hasValue(event) && event.value < 0) {
sink(new Bacon.Error("Value below zero"));
return sink(end());
} else {
return sink(event);
}Note that it's important to return the value from sink so that
the connection to the underlying stream will be closed when no more
events are needed.
Sets the structured description of the observable. The toString and inspect methods
use this data recursively to create a string representation for the observable. This method
is probably useful for Bacon core / library / plugin development only.
For example:
var src = Bacon.once(1) var obs = src.map(function(x) { return -x }) console.log(obs.toString()) --> Bacon.once(1).map(function) obs.withDescription(src, "times", -1) console.log(obs.toString()) --> Bacon.once(1).times(-1)
The method returns the same observable with mutated description.
Creates an EventStream/Property by sampling a given samplee
stream/property value at each event from the this stream/property.
type of values in the samplee
type of values in the result
function to select/calculate the result value based on the value in the source stream and the samplee
Lets you run a state machine on an observable. Give it an initial state object and a state transformation function that processes each incoming event and returns an array containing the next state and an array of output events. Here's an example where we calculate the total sum of all numbers in the stream and output the value on stream end:
Bacon.fromArray([1,2,3])
.withStateMachine(0, function(sum, event) {
if (event.hasValue)
return [sum + event.value, []]
else if (event.isEnd)
return [undefined, [new Bacon.Next(sum), event]]
else
return [sum, [event]]
})type of machine state
type of values to be emitted
initial state for the state machine
the function that defines the state machine
Returns an EventStream with elements pair-wise lined up with events from this and the other EventStream or Property. A zipped stream will publish only when it has a value from each source and will only produce values up to when any single source ends.
The given function f is used to create the result value from value in the two
sources. If no function is given, the values are zipped into an array.
Be careful not to have too much "drift" between streams. If one stream produces many more values than some other excessive buffering will occur inside the zipped observable.
Example 1:
var x = Bacon.fromArray([1, 2])
var y = Bacon.fromArray([3, 4])
x.zip(y, function(x, y) { return x + y })
# produces values 4, 6See also zipWith and zipAsArray for zipping more than 2 sources.
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Observable is the base class for EventsStream and Property