https://github.com/watson/secret-event-listener

Add an event listener without causing any side effects
https://github.com/watson/secret-event-listener

Last synced: about 2 months ago
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Add an event listener without causing any side effects

• Host: GitHub
• URL: https://github.com/watson/secret-event-listener
• Owner: watson
• License: mit
• Created: 2018-06-25T11:59:02.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2018-06-25T12:16:51.000Z (over 6 years ago)
• Last Synced: 2024-05-12T06:40:43.528Z (5 months ago)
• Language: JavaScript
• Size: 6.84 KB
• Stars: 34
• Watchers: 4
• Forks: 5
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# secret-event-listener

Add an event listener without causing any side effects.

[![npm](https://nodei.co/npm/secret-event-listener.png)](https://www.npmjs.com/package/secret-event-listener)

[![Build status](https://travis-ci.org/watson/secret-event-listener.svg?branch=master)](https://travis-ci.org/watson/secret-event-listener)

[![js-standard-style](https://img.shields.io/badge/code%20style-standard-brightgreen.svg?style=flat)](https://github.com/feross/standard)

## Why?

Adding an event listener to an emitter object will normally trigger

certain side effects. E.g. the

[`newListener`](https://nodejs.org/api/events.html#events_event_newlistener)

event will be emitted for every new listener added. A

`MaxListenersExceededWarning` process warning will be emitted if the

emitter reaches is [maximum listener

count](https://nodejs.org/api/events.html#events_emitter_setmaxlisteners_n).

Or a readable stream will enter [flowing

mode](https://nodejs.org/api/stream.html#stream_two_modes) if a `data`

listener is added.

This module gives you the ability to attach a listener without

triggering any of these side effects.

**Only use this module if you are sure you don't want any side effects

and there's other way to achieve your goals!**

## Installation

```

npm install secret-event-listener --save

```

## Usage

```js

const {EventEmitter} = require('events')

const addSecretListener = require('secret-event-listener')

const emitter = new EventEmitter()

emitter.on('newListener', function () {

  throw new Error('should not fire the newListener event!')

})

addSecretListener(emitter, 'foo', function () {

  console.log('foo event fired :)')

})

emitter.emit('foo')

```

## API

### `addSecretListener(emitter, eventName, listener)`

Arguments:

- `emitter` - an object inheriting from

  [`EventEmitter`](https://nodejs.org/api/events.html#events_class_eventemitter)

- `eventName` - the event to add the `listener` to

- `listener` - a listener function which should be called every time an

  event of `eventName` is emitted.

### `addSecretListener.prepend(emitter, eventName, listener)`

Like the main `addSecretListener` function, except the `listener` is

added to the beginning of the listeners array for the event named

`eventName`. 

## License

[MIT](https://github.com/watson/secret-event-listener/blob/master/LICENSE)