R6 class to emit some event

This is a general purpose class to build on. It is inspired by the node.js EventEmitter class. See https://nodejs.org/api/events.html.

Methods

Public methods

• EventEmitter$emit()

• EventEmitter$on()

• EventEmitter$addListener()

• EventEmitter$once()

• EventEmitter$listenerCount()

• EventEmitter$eventNames()

• EventEmitter$rawListeners()

• EventEmitter$listeners()

• EventEmitter$clone()

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Method emit()

Usage

EventEmitter$emit(eventName, ...)

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Method on()

Usage

EventEmitter$on(eventName, listener)

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Method addListener()

Usage

EventEmitter$addListener(eventName, listener)

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Method once()

Usage

EventEmitter$once(eventName, listener)

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Method listenerCount()

Usage

EventEmitter$listenerCount(eventName)

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Method eventNames()

Usage

EventEmitter$eventNames()

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Method rawListeners()

Usage

EventEmitter$rawListeners(eventName)

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Method listeners()

Usage

EventEmitter$listeners(eventName)

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Method clone()

The objects of this class are cloneable with this method.

Usage

EventEmitter$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Examples

myEmitter <- EventEmitter$new()
myEmitter$on("event",
    function() {
        message("an event occured!")
    }
)
myEmitter$emit("event")
#> an event occured!
# The listener is still called when "event" fires:
myEmitter$emit("event")
#> an event occured!
# A listener can be registered once:
myEmitter$once("event",
    function() {
        message("this listener is called only once")
    }
)
# This new listener will be removed when called.
myEmitter$emit("event")
#> an event occured!
#> this listener is called only once
# There is now only one listener:
myEmitter$emit("event")
#> an event occured!

# An error in a listener will throw an error in R.
myEmitter$on("event", function(...) stop("An error in a listener"))
# Throw an error:
if (FALSE) {
  myEmitter$emit("event")}

# You can catch an error with a special "error" event that is
# always emitted when an error occured in a listener:
myEmitter$on("error", function(e) cat(conditionMessage(e)))
myEmitter$emit("event")
#> an event occured!
#> An error in a listener

# As in the node.js class, a "newListener" event is emitted
# before each new listener registration.
# The "newListener" event passes two arguments to its listener(s):
# `eventName` and `listener`.
myEmitter <- EventEmitter$new()
# Use once here to avoid infinite recursion:
myEmitter$once("newListener", function(eventName, listener) {
   if(eventName == "event") {
      myEmitter$on("event", function(...) cat("B"))
   }
})
myEmitter$on("event", function(...) cat("A"))
myEmitter$emit("event") # BA
#> BA
# The listener attached to the "newListener" event has been
# unregistered and is no more called:
myEmitter$on("event", function(...) cat("C"))
myEmitter$emit("event") # BAC
#> BAC

# Get the number of listeners for an event:
myEmitter$listenerCount("event")
#> [1] 3

# Get the event names which have been registered:
myEmitter$eventNames()
#> [1] "event"