@to1source/event

An universal Event Emitter / Bus for Javascript.

This package was nb-event-service and now we move under @to1source/event namespace to continue the development.

There is no dependency for this package.

Installation

$ npm install @to1source/event

This module works in browser as well as node.js.

The main different between this module and the other event emitter out there is this:

We don't care about the order of event registration and handling

Basically you can trigger an event that doesn't exist (well, sort of, its magic)

For example:

//  other library like EventEmitter
ee.emitEvent('someEvent')

ee.addListener('someEvent', function() {
  console.log('I am called')
})

The callback in the above example never works and you will never see the message. But our can do it:

es.$trigger('someEvent', 'Hello world!') // <-- not yet exist

ee.$on('someEvent', function(msg) {
  console.log(msg)
})

The above message will show (as soon as you register the event name with a handler)

Please note the module is using ES6+ (WeakMap, Set, Map, Array.from etc). When you use this module on older browser, please provide polyfill accordingly

When you include this module in browser (using our stock build). You will get a To1SourceEvent global object:

<script>
  var event = new To1SourceEvent()
  // then do your thing
</script>

API

$on(eventName, callback, context)

• eventName (string) The event name you want to handle. You can call this multiple times to add different listeners
• callback (function) it will receive the params that call
• context (object|null) optional, we will pass it like this Reflect.apply(callback, context, args)

It will return the total number of events that get registered.

$once(eventName , callback, context)

• eventName (string) the event you want to listen to once, you can call this more than once to add more listener
• callback (function) it will receive the params that call
• context (object|null) optional same as above

$once allow you to bind one or more listener to the same event. But once this event fired (triggered) it will remove itself from the event store, and no longer available. This behavior is changed in V1.3.0.

There is a potential problem with $once you can see below. It's not really a bug per se, but due to our own unique feature that can call event before it existed (yeah, it's kinda magic)

// trigger event before it register with a handler
ee.$trigger('someEvent')
// now it register with a regular $on
ee.$on('someEvent', function() {
  console.log('call me second')
})
// but some where else you try to register it with $once
ee.$once('someEvent', function() {
  console.log('call me first')
})

You can register more than one handler.

Take a look at the above example, you register it with $on then $once.

What happen is, the $once call execute by the $trigger from the earlier call, then it will remove this event from the event handler store. Therefore, your $on will never fire again.

So you have to make sure which event you REALLY want to register with what.

$only(eventName , callback, context)

• eventName (string) the event you want to listen to once, this is first come first serve, and only ONE listener
• callback (function) it will receive the params that call
• context (object|null) optional same as above

Example:

es.$only('only-event', function(message) {
  console.log('ONLY', message)
})
// now if you try to add another
es.$only('only-event', function(message) {
  console.log('AGAIN', message)
})

// execute it
es.$trigger('only-event', 'A little cat jumping through the window')

You will only get ONLY A little cat jumping through the window but the second callback never add to the event store. Although we develop this feature purposely for our other library to use, but it has a lot real world usage.

$onlyOnce(eventName , callback, context)

Just like what it said on the tin; its $only + $once. You should able to figure out what it does.

$off(eventName)

• eventName (string) event to remove from internal store

It will return

• true - event been clear
• false - such event doesn't exist

$replace(eventName, callback, context = null, type = 'on')

This is $off + event register function

Type can be on, only, once, onlyOnce default value is on

$trigger(eventName, params , context, type)

• eventName (string) this will trigger the callback that register with this eventName whether that actually exist or not
• params (mixed) optional - data you want to pass to your callback method
• context (object || null) optional - When we execute the callback, we will add this context to the Reflect.apply or default to null
• type (string) available types are on, only, once, onlyOnce this is for trigger event before it get register and prevent other type to register it

This method will return:

• false - if there is nothing to call
• i - the total number of event been called

$call(eventName, type, context) => (...params)

It takes three parameter then return a function to accept the parameters

• eventName (string) this will trigger the callback that register with this eventName whether that actually exist or not
• type (string) optional - available types are on, only, once, onlyOnce this is for trigger event before it get register and prevent other type to register it
• context (object || null) optional - When we execute the callback, we will add this context to the Reflect.apply or default to null

Then the return function will accept parameter as spread. Internally it calls $trigger, but the return function accept parameter as spread to prevent an edge case, when you only have one parameter but it's an array. The spread will make sure it's an array of any type (in the edge case it will be array of an array) and the data will pass to the call back correctly.

Example:

// call before event register
es.$call('some-event', 'only')(1001, 2000) // note the function call
// now try to register it with a different event handler
es.$on('some-event', function someEventCallback(num, more) {
  return num + more
})
// it will throw Error that tells you it has been register with `only` type already

$max(evt, max) => (...args)

This method let you execute a particular call back ($on or $only type, because they can get call repeatedly) up to max time.

To use this method, first you need to register an event with $on or $only. It doesn't work with non-registered event. Then you pass the event name and max number, and you will get a function back to execute the call. For example:

import Event from '@to1source/event'

const evtCls = new Event()
const evtName = 'some-event-for-testing'

// set up the event callback
evtCls.$on(evtName, value => ++value)

// next setup the max call
const countDownFn = evtClass.$max(evtName, 2) // can call it twice

let numberOfCallLeft  

numberOfCallLeft = countDownFn(100)
// value is 1
numberOfCallLeft = countDownFn(10000)
// value is now -1
countDownFn(100000) // this will have no effect, because the event already remove from internal store

Several things to remember:

• If you call $trigger or $call in between, they won't be counted. This method only register the number of its own call
• After the count reach max, it will remove the event from the store, and you won't able to call it again
• when it returns -1 then you can not call it anymore, or an integer below your initial max value, because every time you call it, it reduces the count by 1 immediately

$get(evt)

It returns all the listeners for that particular event name from the internal store. Handy for debug.

Or it will return false if there is nothing

$suspend / $release

When you call $suspend , all the $trigger and $call action will have no effect and put into a temporary store, and wait until you call $release. This is an on / off switch no in between.

const evtSrv = new To1SourceEvent()

evtSrv.$on('some-event', value => {
  return value + 1
})

evtSrv.$suspend() // suspend all events from this point onward

evtSrv.$trigger('some-event', 100)
// what happen inside
console.log(evtSrv.$done) // null

evtSrv.$release() // release all the event that has been suspended
// what happen now
console.log(evtSrv.$done) // 101

$suspendEvent(eventNamePattern)

This is similar to $suspend, but it allows you to provide an event name pattern to those event name that matches. It allow you to add mutliple eventNamePattern. Important to note that, if $suspend has been called, this method has no effect.

const evtSrv = new To1SourceEvent()

evtSrv.$on('some-event-ok', () => {
  console.log('ok')
})

evtSrv.$on('some-event-not-great', () => {
  console.log('Not great!')
})
// @NOTE you can pass the entire event name or just part that can match
evtSrv.$suspendEvent(`-not-great`)
// or pass an RegExp object
evtSrv.$suspendEvent(/\-not-great/) // note the second call will overwrite the first one

evtSrv.$trigger('some-event-ok')
evtSrv.$trigger('some-event-not-great')

// $release() --> when you can $release, the previous block event will get executed

In the above example, only the some-event-ok will get triggered.

If you call $release instead, then everything will get release at once.

Also you can pass as many pattern as you want

evtSrv.$suspendEvent(`event-to-suspend-1`, `event-to-suspend-2`)

$releaseEvent(eventNamePattern)

This is the opposite of the $suspendEvent; it will release those suspend events if it matches the eventNamePattern. It will return the number of the released event from queue. And it's the same like $suspendEvent, if $suspend already been called; it has no effect.

const evtSrv = new To1SourceEvent()

evtSrv.$on('some-event-ok', () => {
  console.log('OK')
})

evtSrv.$on('some-event-not-great', () => {
  console.log('Not great!')
})

evtSrv.$on('the-usa-is-not-great', () => {
  console.log(`USA sucks!`)
})

evtSrv.$on('some-other-event-name', () => {
  console.log(`I will not get affected and continue to work as it was expected`)
})

// @NOTE you can pass the entire event name or just part that can match
evtSrv.$suspendEvent(`-not-great`)
// or pass an RegExp object
evtSrv.$suspendEvent(/\-not-great/) // note the second call will overwrite the first one

evtSrv.$trigger('some-event-ok') // this will get exeucted

evtSrv.$trigger('some-event-not-great') // this will not get exeucted

evtSrv.$trigger('some-other-event-name') // this will get execute

const ctn = evtSrv.$releaseEvent(`-not-great`) // now anything with *-not-great will get released

Also you can release multiple event like so:

evtSrv.$releaseEvent(`event-to-release-1`, `event-to-release-2`)

$debug(idx)

This method only logging output, so make sure you have passed a logger when you create the class instance.

• 0 lazyStore
• 1 normalStore

If you don't pass anything, it will log all the stores to show what is inside.

Alias version

If you don't like the $, you can use the alias version.

• browser you can include the dist/to1source-event.alias.js
• ES6 import To1SourceEvent from '@to1source/event/alias'
• node you can require('@tosource/event/dist/alias')

And that will gives you the following alias version:

• on --> $on
• once --> $once
• off --> $off
• emit --> $trigger
• get --> $get
• only --> $only
• onlyOnce --> $onlyOnce
• replace --> $replace

If you want everything alias, then roll your own by extending this class

// node
import To1SourceEvent from '@to1source/event/alias'

class MyEventClass extends To1SourceEvent {
  constructor(config) {
    super(config)
  }

  // you can overwrite the $name getter to give yourself a new name
  get $name() {
    return 'roll-my-own-event-class'
  }

  // then do more of your alias
  // example
  suspend() {
    return this.$suspend()
  }

  // or something like this
  suspendEvent(...args) {
    return Reflect.apply(this.$suspendEvent, this, args)
  }
}

$done getter

This should return the last value that get exeucted

Whenever you execute the callback, the result will store in the internal $done setter.

So you can call the $done getter to get back the last result.

Example:

es.$on('add', function add(val) {
  return val + 1
})

es.$trigger('add', 1000)

console.log(es.$done) // should see a 1001

You will get a 1001. This might be useful in some situation. Please note, it will get call whenever an event gets trigger; if at the same time some other event trigger, then your value might be different from what you expected. So use this with caution.

Types for typescript

V.2 completely rewritten with Typescript, and have tsc generate all the correct type files. V.1.5.0 add type definition to the project @types/index.d.ts and its included in the package.json.

Test

We use ava for testing.

$ npm test  

Build

We use rollup for building process. V.2 use esbuild to build the package directly. Might move back to rollup if require in the future.

$ npm run build

---

UNLICENSED

TO1SOURCE / Joel Chu / NEWBRAN LTD (c) 2023