eventemitter-callback

Emit an event and waiting for a result. Based on eventemitter3.

Installation

By package manager:

npm install eventemitter-callback --save

# For Yarn, use the command below.
yarn add eventemitter-callback

Installation from CDN:

<!-- For UNPKG use the code below. -->
<script src="https://unpkg.com/eventemitter-callback"></script>

<!-- For JSDelivr use the code below. -->
<script src="https://cdn.jsdelivr.net/npm/eventemitter-callback"></script>

<script>
  // UMD module is exposed through the "EventEmitterCB" global variable.
  console.log(EventEmitterCB);
</script>

Usage

import emitter from 'eventemitter-callback'
// import * as emitter from 'eventemitter-callback' // type: 'module'

emitter.on('event-name', (arg) => {
  console.log(arg) // prints "ping"
  return 'pong'
})

// emit an event and waiting for its result
emitter.emit('event-name', 'ping', (arg) => {
  console.log(arg) // prints "pong"
})

Disable triggering events before listening

By default, the following works normally:

emitter.emit('msg', 1)
emitter.on('msg', (arg) => {
  console.log(arg) // prints 1
})

If this doesn't meet your expectations, you can disable it:

emitter.disablePreEmitter();
emitter.emit('msg', 1)
emitter.on('msg', (arg) => {
  console.log(arg) // will not be called!
})

API

• on(eventName, listener)
• once(eventName, listener)
• emit(eventName[, ...args][, callback])
• emitAll(eventName[, ...args])
• emitValidateAll(eventName[, ...args])
• emitValidateAnyOf(eventName[, ...args])
• off(eventName[, listener])
• disablePreEmitter()
• enablePreEmitter()

on(eventName, listener)

Adds the listener function to the end of the listeners array for the event named eventName.

• eventName string the name of the event
• listener function the callback function

The listener can be asynchronous. Specified as an AsyncFunction or return a Promise.

emitter.on('event-name', (arg) => {
  console.log(arg) // prints "ping"
  return new Promise((resolve) => {
    resolve('pong')
  })
})
// emitter.on('event-name', async (arg) => {
//   console.log(arg) // prints "ping"
//   const res = await queryRemote() // suppose res returns 'pong'
//   return res
// })
emitter.emit('event-name', 'ping', (arg) => {
  console.log(arg) // prints "pong"
})

once(eventName, listener)

• eventName string the name of the event
• listener function the callback function

Adds a one-time listener function for the event named eventName.

emit(eventName[, ...args][, callback])

• eventName string the name of the event
• ...args any
• callback any the callback function

Returns true if the event had listeners, false otherwise.

emitAll(eventName[, ...args])

• eventName string the name of the event
• ...args any

Trigger all the listeners at once. Returns a result array by Promise.all.

emitValidateAll(eventName[, ...args])

• eventName string the name of the event
• ...args any

Trigger all the listeners at once and check the values returned. Returns true if all listeners returns true, false otherwise.

emitValidateAnyOf(eventName[, ...args])

• eventName string the name of the event
• ...args any

Trigger all the listeners at once and check the values returned. Returns true if either listener returns true, false otherwise.

off(eventName[, listener])

• eventName string the name of the event
• listener function the callback function

Removes the specified listener from the listener array for the event named eventName.

Removes all the listeners for the event:

emitter.off('event-name')

disablePreEmitter()

Disable triggering events before listening.

enablePreEmitter()

Enable triggering events before listening.

emitter._eventEmitter

Reference to current instance of EventEmitter3.

emitter._EventEmitter

Reference to constructor of EventEmitter3.

License

MIT, see the LICENSE file for detail.