hook-emitter

Event emitter with support for asynchronous handlers and a sweet "hook" mechanism.

Note: hook-emitter requires Node.js 4 or newer.

Installation

npm install hook-emitter

Examples

Async listener example:

import { HookEmitter } from 'hook-emitter';
// the CommonJS way:
// const HookEmitter = require('hook-emitter').HookEmitter;

const emitter = new HookEmitter();

emitter.on('sum', (x, y) => {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('the sum of ' + x + ' + ' + y + ' = ' + (x + y));
            resolve();
        }, 100);
    });
});

emitter.emit('sum', 3, 7);

Hook example:

const emitter = new HookEmitter();

const hookedSum = emitter.hook('sum', (x, y) => {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            // x = 6, y = 14
            resolve(x + y);
        }, 100);
    });
});

emitter.on('sum', evt => {
    console.log('doubling x and y');
    evt.args[0] *= 2;
    evt.args[1] *= 2;
});

hookedSum(3, 7)
    .then(result => {
        console.log('The sum of 6 + 14 = ' + result);
    })
    .catch(err => console.error);

Chaining multiple hooked functions example:

const emitter = new HookEmitter();

Promise.resolve()
    .then(emitter.hook('step1', () => {
        console.log('step 1');
    }))
    .then(emitter.hook('step2', () => {
        console.log('step 2');
    }))
    .then(emitter.hook('step3', () => {
        console.log('step 3');
    }))
    .catch(err => console.error);

API

Constructor

The HookEmitter constructor takes no arguments.

Properties

events

A Map object of event names to arrays of listener functions. This can be iterated over using a for-of loop.

Methods

on(event, listener)

Adds an event listener. Returns this.

• event String - One or more space-separated event names to add the listener to.
• listener Function - A function to call when the event is emitted.

once(event, listener)

Adds an event listener that will only be called once. Returns this.

• event String - One or more space-separated event names to add the listener to.
• listener Function - A function to call when the event is emitted.

off(event, listener)

Removes an event listener. Returns this.

• event String - One or more space-separated event names to remove the listener from.
• listener Function (optional) - The listener function. If not specified, then all listeners for the specified event are removed.

emit(event, ...args)

Emits one or more events. Returns a Promise.

• event String - The name of the event to emit.
• args * (optional) - One or more additional arguments to be emitted with the event.

hook(event, ctx, fn)

Creates a function hook. Returns a Function which when called returns a Promise.

• event String - The name of the hook's event.
• ctx Object (optional) - The context to run the function in. Useful if fn is going to be overwritten.
• fn Function - The function being hooked up.

License

(The MIT License)

Copyright (c) 2015-2016 Chris Barber

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.