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# Nitt
> Small functional event emitter / pubsub.
* **Microscopic:** weighs less than 200 bytes gzipped
* **Useful:** a wildcard `"*"` event type listens to all events
* **Familiar:** same names & ideas as [Node's EventEmitter](https://nodejs.org/api/events.html#events_class_eventemitter)
nitt was made for the browser, but works in any JavaScript runtime. It has no dependencies and supports IE9+.
## Table of Contents
* [Install](#install)
* [Usage](#usage)
* [Examples & Demos](#examples--demos)
* [API](#api)
* [Contribute](#contribute)
* [License](#license)
## Install
This project uses [node](http://nodejs.org) and [npm](https://npmjs.com). Go check them out if you don't have them locally installed.
```sh
$ npm install --save nitt
```
Then with a module bundler like [rollup](http://rollupjs.org/) or [webpack](https://webpack.js.org/), use as you would anything else:
```javascript
// using ES6 modules
import nitt from 'nitt'
// using CommonJS modules
var nitt = require('nitt')
```
The [UMD](https://github.com/umdjs/umd) build is also available on [unpkg](https://unpkg.com):
```html
<script src="https://unpkg.com/nitt/dist/nitt.umd.js"></script>
```
You can find the library on `window.nitt`.
## Usage
```js
import nitt from 'nitt'
const emitter = nitt()
// listen to an event
emitter.on('foo', e => console.log('foo', e) )
// listen to all events
emitter.on('*', (type, e) => console.log(type, e) )
// fire an event
emitter.emit('foo', { a: 'b' })
// clearing all events
emitter.all.clear()
// working with handler references:
function onFoo() {}
emitter.on('foo', onFoo) // listen
emitter.off('foo', onFoo) // unlisten
```
### Typescript
Set `"strict": true` in your tsconfig.json to get improved type inference for `nitt` instance methods.
```ts
import nitt from 'nitt';
type Events = {
foo: string;
bar?: number;
};
const emitter = nitt<Events>(); // inferred as emitter<Events>
emitter.on('foo', (e) => {}); // 'e' has inferred type 'string'
emitter.emit('foo', 42); // Error: Argument of type 'number' is not assignable to parameter of type 'string'. (2345)
```
Alternatively, you can use the provided `emitter` type:
```ts
import nitt, { emitter } from 'nitt';
type Events = {
foo: string;
bar?: number;
};
const emitter: emitter<Events> = nitt<Events>();
```
## API
<!-- Generated by documentation.js. Update this documentation by updating the source code. -->
#### Table of Contents
* [nitt](#nitt)
* [all](#all)
* [on](#on)
* [Parameters](#parameters)
* [off](#off)
* [Parameters](#parameters-1)
* [emit](#emit)
* [Parameters](#parameters-2)
* [once](#once)
* [Parameters](#parameters-3)
* [when](#when)
* [Parameters](#parameters-4)
### nitt
Nitt: Tiny (~200b) functional event emitter / pubsub.
Returns **Nitt** 
### all
A Map of event names to registered handler functions.
### on
Register an event handler for the given type.
#### Parameters
* `type` **([string](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String) | [symbol](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Symbol))** Type of event to listen for, or `'*'` for all events
* `handler` **[Function](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function)** Function to call in response to given event
### off
Remove an event handler for the given type.
If `handler` is omitted, all handlers of the given type are removed.
#### Parameters
* `type` **([string](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String) | [symbol](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Symbol))** Type of event to unregister `handler` from (`'*'` to remove a wildcard handler)
* `handler` **[Function](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function)?** Handler function to remove
### emit
Invoke all handlers for the given type.
If present, `'*'` handlers are invoked after type-matched handlers.
Note: Manually firing '\*' handlers is not supported.
#### Parameters
* `type` **([string](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String) | [symbol](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Symbol))** The event type to invoke
* `evt` **Any?** Any value (object is recommended and powerful), passed to each handler
### once
Register an event handler that is executed just once for the given type.
#### Parameters
* `type` **([string](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String) | [symbol](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Symbol))** Type of event to listen for, or `'*'` for all events
* `handler` **[Function](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function)** Function to call in response to given event
### when
Returns a promise for a single event
#### Parameters
* `type` **[String](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String)** Type of event to listen for, or `"*"` for any event
Returns **[Promise](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise)\<any>** 
## Contribute
For reporting issues and submitting patches, send an email.
## License
[MIT License](https://opensource.org/licenses/MIT)
|
