event-e3
v8.1.3
Published
Universal light Event Emitter
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event-e3
Event Emitter 3
Installation
import
// Deno
import Emitter from 'https://unpkg.com/event-e3/event-e3.js'
// rollup webpack typescript, node12+
import Emitter from "event-e3";
// raw import
import Emitter from "./node_modules/event-e3/event-e3.js";
// with require()
const Emitter = require("event-e3/built/event-e3.js");
API
eventName
must be a string or a symbol
Emitter
As a decorator:
const user = Emitter({ name: 'tobi' });
As an instance:
const emitter = new Emitter();
.on(eventName, fn)
Register an eventName
handler fn
.
.emit(eventName, data)
Emit an event eventName
with data. Will trigger previously registered handlers
.once(eventName, fn)
Register a single-shot eventName
handler fn
, removed immediately after it is invoked the first time.
.off(eventName, fn)
- Pass
eventName
andfn
to remove a listener. - Pass
eventName
to remove all listeners on that eventName. - Pass nothing to remove all listeners on all events.
.listeners(eventName)
Return an array of callbacks, or an empty array.
.hasListeners(eventName)
True if this emitter has any eventName
handlers.
.eventNames()
Returns an array listing the events for which the emitter has registered listeners.
.eventNamesStrings()
Same as .eventNames()
but the array is only Strings.
EmitterListener
EmitterListener exposes a way to subscribe to subscriptions and unsubscriptions. It can only be used as a constructor, example usage:
import {EmitterListener, onSubscribe, onUnsubscribe} from "event-e3/source/EmitterListener.js";
const x = new EmitterListener();
x.on(onSubscribe, console.log.bind('console', 'on\'ed'))
x.on(onUnsubscribe, console.log.bind('console', 'off\'ed'))
EmitterListenerPlus
EmitterListener further extends EmitterListener. It can be used to direclty listen for the first subscription and last unsubscription for a given event name and It can only be used as a constructor, example usage:
import {EmitterListenerPlus, onFirstSubscribe, onLastUnsubscribe, onSubscribe, onUnsubscribe} from "event-e3/source/EmitterListenerPlus.js";
const x = new EmitterListenerPlus();
x.on(onFirstSubscribe, console.log.bind('console', 'on\'ed'))
x.on(onLastUnsubscribe, console.log.bind('console', 'off\'ed'))
RegularListener
Extends EmitterListenerPlus, also emits onFirstSubscribeString
and onLastUnsubscribeString
filterEventStream
Makes it convenient to filter an event stream. The new event stream is emitted on the same emitter as regular events.
An example use case: An Emitter emits 'Earthquake' for the scientific community. But the general public is interested in big ones only.
import Emitter from "event-e3";
import {filterEventStream} from "event-e3/source/filterEventStream.js";
const earthQuakeEmitter = Emitter({});
const isBigEarthQuake = earthQuake => earthQuake.richterScale > 6;
filterEventStream(earthQuakeEmitter, 'Earthquake', 'BigEarthQuake', isBigEarthQuake);
// the original event is still emitted
earthQuakeEmitter.on('Earthquake', scientificCommunity.study);
// 'BigEarthQuake' happens sometimes
earthQuakeEmitter.on('BigEarthQuake', newsAggregator.publishNews);
earthQuakeEmitter.on('BigEarthQuake', humanHelpWithoutBorders.organize);
Comparison with NodeJs Event Emitter
this
is undefined inside the event handler- error events do not trigger any special logic
- no captureRejections
- no maxListener
.emit
can only emit 1 thing (use array or object for more)- no prepend
- no method aliases
- no dependencies
Tests
npm t