Ascend Events

Installation

// npm
npm install ascend-events

// yarn
yarn install ascend-events

API

EventEmitter

Create an Event Emitter.

import { EventEmitter } from 'ascend-events';

// New EventEmitter
const eventEmitter = new EventEmitter();

// Extend a custom class
class MyClass extends EventEmitter {
    constructor() {
        super();
    }
}

addListener

Adds a new event listener to the end of the listener array that is associated with the passed eventName. If no key is found, it will set a new element using the passed eventName and listener.

params

• eventName {string} | {symbol} (required) The name of the event being added
• listener {Function} (required) The callback function

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.addListener('listener', () => console.log('listener'));

emit

Calls each listener associated with the passed eventName in the order that they were added. Additional arguments are passed to each listener callback.

params

• eventName {string} | {symbol} (required) The name of the event being emitted
• ...args {any[]} (Optional) Arguments to be passed to each listener function

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.add('test', (msg: string) => console.log('msg: ', msg));

eventEmitter.emit('test', 'hello world');

// prints 'msg: hello world'

getListenerCount

Returns the number of listeners associated with the passed eventName.

params

• eventName {string} | {symbol} (required) The name of the event to get the listener count of

returns

• {number}

const eventEmitter = new EventEmitter();

eventEmitter.addListener('msg', (msg: msg) => console.log('msg: ', msg));

eventEmitter.getListenerCount('msg'); // returns 1
eventEmitter.getListenerCount('doesntExist'); // returns 0

setMaxListeners

Sets the maximum number of listeners on this instance of the EventEmitter.

params

• num {number} (required) The number of maximum listeners

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.setMaxListeners(5);

console.log(eventEmitter.maxListeners); // prints 5

listeners

Returns the listeners associated with the passed eventName, if no key was found, returns an empty array [].

params

• eventName {string} | {symbol} (required)

returns

• listeners {Listener[]}

const eventEmitter = new EventEmitter();

eventEmitter.addListener('event', () => null)

eventEmitter.listeners('event') // returns [ { fn: [Function], once: false } ]

off

alias for EventEmitter.removeListener()

params

• eventName {string} | {symbol} (required)
• listener {Function} (required)

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.on('msg', (msg: string) => console.log('msg: ', msg));

eventEmitter.off('msg', (msg:string) => console.log('msg: ', msg));

on

alias for eventEmitter.addListener()

params

• eventName {string} | {symbol} (required)
• listener {Function} (required)

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.on('msg', (msg: string) => console.log('msg: ', msg));

eventEmitter.emit('msg', 'hello world');

once

Adds a listener associated to the passed eventName that is triggered once and then removed.

params

• eventName {string} | {symbol} (required)
• listener {Function} (required)

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.once('msg', (msg: string) => console.log('msg: ', msg));

eventEmitter.emit('msg', 'hello world'); // prints 'msg: hello world'

eventEmitter.listeners('msg'); // returns []

prependListener

Adds the passed listener to the beginning of the listener array associated with the given eventName.

params

• eventName {string} | {symbol} (required)
• listener {Function} (required)

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.addListener('msg', () => 'called second');

eventEmitter.prependListener('msg', () => 'called first');

eventEmitter.emit('msg');
// prints
//  'called first'
//  'called second'

prependOnceListener

Adds the passed listener to the beginning of the listener array associated with the given eventName, once triggered will be removed.

params

• eventName {string} | {symbol} (required)
• listener {Function} (required)

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.prependOnceListener('msg', () => 'One time');

eventEmitter.emit('msg');

eventEmitter.listeners('msg'); // returns []

removeAllListeners

Removes all listeners associated with the passed eventName, if no eventName was given, all listeners are removed entirely.

params

• eventName {string} | {symbol} (optional)

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.addListener('msg', () => console.log('gets removed'));
eventEmitter.addListener('msg2', () => console.log('also gets removed'));

eventEmitter.removeAllListeners();

removeListener

Removes listener associated with the passed eventName

params

• eventName {string} | {symbol} (required)
• listener {Function} (required)

returns

• this {EventEmitter}

const eventEmitter = new EventEmitter();

eventEmitter.addListener('msg', () => console.log('gets removed'));
eventEmitter.addListener('msg', () => console.log('does not get removed'));

eventEmitter.removeListener('msg', () => console.log('gets removed'));

eventEmitter.emit('msg'); //  prints 'does not get removed'