| # EventEmitter3 | |
| [](https://www.npmjs.com/package/eventemitter3)[](https://travis-ci.org/primus/eventemitter3)[](https://david-dm.org/primus/eventemitter3)[](https://coveralls.io/r/primus/eventemitter3?branch=master)[](https://webchat.freenode.net/?channels=primus) | |
| [](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. | |
| Note that you will have to run an additional `npm i` in the benchmarks folder | |
| before `npm run benchmark`. | |
| ## License | |
| [MIT](LICENSE) | |