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- # EventEmitter3
-
- [![Version npm](https://img.shields.io/npm/v/eventemitter3.svg?style=flat-square)](https://www.npmjs.com/package/eventemitter3)[![Build Status](https://img.shields.io/travis/primus/eventemitter3/master.svg?style=flat-square)](https://travis-ci.org/primus/eventemitter3)[![Dependencies](https://img.shields.io/david/primus/eventemitter3.svg?style=flat-square)](https://david-dm.org/primus/eventemitter3)[![Coverage Status](https://img.shields.io/coveralls/primus/eventemitter3/master.svg?style=flat-square)](https://coveralls.io/r/primus/eventemitter3?branch=master)[![IRC channel](https://img.shields.io/badge/IRC-irc.freenode.net%23primus-00a8ff.svg?style=flat-square)](https://webchat.freenode.net/?channels=primus)
-
- [![Sauce Test Status](https://saucelabs.com/browser-matrix/eventemitter3.svg)](https://saucelabs.com/u/eventemitter3)
-
- EventEmitter3 is a high performance EventEmitter. It has been micro-optimized
- for various of code paths making this, one of, if not the fastest EventEmitter
- available for Node.js and browsers. The module is API compatible with the
- EventEmitter that ships by default with Node.js but there are some slight
- differences:
-
- - Domain support has been removed.
- - We do not `throw` an error when you emit an `error` event and nobody is
- listening.
- - The `newListener` and `removeListener` events have been removed as they
- are useful only in some uncommon use-cases.
- - The `setMaxListeners`, `getMaxListeners`, `prependListener` and
- `prependOnceListener` methods are not available.
- - Support for custom context for events so there is no need to use `fn.bind`.
- - The `removeListener` method removes all matching listeners, not only the
- first.
-
- It's a drop in replacement for existing EventEmitters, but just faster. Free
- performance, who wouldn't want that? The EventEmitter is written in EcmaScript 3
- so it will work in the oldest browsers and node versions that you need to
- support.
-
- ## Installation
-
- ```bash
- $ npm install --save eventemitter3
- ```
-
- ## CDN
-
- Recommended CDN:
-
- ```text
- https://unpkg.com/eventemitter3@latest/umd/eventemitter3.min.js
- ```
-
- ## Usage
-
- After installation the only thing you need to do is require the module:
-
- ```js
- var EventEmitter = require('eventemitter3');
- ```
-
- And you're ready to create your own EventEmitter instances. For the API
- documentation, please follow the official Node.js documentation:
-
- http://nodejs.org/api/events.html
-
- ### Contextual emits
-
- We've upgraded the API of the `EventEmitter.on`, `EventEmitter.once` and
- `EventEmitter.removeListener` to accept an extra argument which is the `context`
- or `this` value that should be set for the emitted events. This means you no
- longer have the overhead of an event that required `fn.bind` in order to get a
- custom `this` value.
-
- ```js
- var EE = new EventEmitter()
- , context = { foo: 'bar' };
-
- function emitted() {
- console.log(this === context); // true
- }
-
- EE.once('event-name', emitted, context);
- EE.on('another-event', emitted, context);
- EE.removeListener('another-event', emitted, context);
- ```
-
- ### Tests and benchmarks
-
- This module is well tested. You can run:
-
- - `npm test` to run the tests under Node.js.
- - `npm run test-browser` to run the tests in real browsers via Sauce Labs.
-
- We also have a set of benchmarks to compare EventEmitter3 with some available
- alternatives. To run the benchmarks run `npm run benchmark`.
-
- Tests and benchmarks are not included in the npm package. If you want to play
- with them you have to clone the GitHub repository.
-
- ## License
-
- [MIT](LICENSE)
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