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[](http://badge.fury.io/js/eventemitter2)
[](https://david-dm.org/asynclyeventemitter2)
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# SYNOPSIS
EventEmitter2 is an implementation of the EventEmitter module found in Node.js. In addition to having a better benchmark performance than EventEmitter and being browser-compatible, it also extends the interface of EventEmitter with additional non-breaking features.
# DESCRIPTION
### FEATURES
- Namespaces/Wildcards.
- Times To Listen (TTL), extends the `once` concept with `many`.
- Browser environment compatibility.
- Demonstrates good performance in benchmarks
```
EventEmitterHeatUp x 3,728,965 ops/sec \302\2610.68% (60 runs sampled)
EventEmitter x 2,822,904 ops/sec \302\2610.74% (63 runs sampled)
EventEmitter2 x 7,251,227 ops/sec \302\2610.55% (58 runs sampled)
EventEmitter2 (wild) x 3,220,268 ops/sec \302\2610.44% (65 runs sampled)
Fastest is EventEmitter2
```
### Differences (Non-breaking, compatible with existing EventEmitter)
- The EventEmitter2 constructor takes an optional configuration object.
```javascript
var EventEmitter2 = require('eventemitter2').EventEmitter2;
var server = new EventEmitter2({
//
// set this to `true` to use wildcards. It defaults to `false`.
//
wildcard: true,
//
// the delimiter used to segment namespaces, defaults to `.`.
//
delimiter: '::',
//
// set this to `true` if you want to emit the newListener event. The default value is `true`.
//
newListener: false,
//
// the maximum amount of listeners that can be assigned to an event, default 10.
//
maxListeners: 20,
//
// show event name in memory leak message when more than maximum amount of listeners is assigned, default false
//
verboseMemoryLeak: false
});
```
- Getting the actual event that fired.
```javascript
server.on('foo.*', function(value1, value2) {
console.log(this.event, value1, value2);
});
```
- Fire an event N times and then remove it, an extension of the `once` concept.
```javascript
server.many('foo', 4, function() {
console.log('hello');
});
```
- Pass in a namespaced event as an array rather than a delimited string.
```javascript
server.many(['foo', 'bar', 'bazz'], function() {
console.log('hello');
});
```
# Installing
`npm install --save eventemitter2`.
# API
When an `EventEmitter` instance experiences an error, the typical action is
to emit an `error` event. Error events are treated as a special case.
If there is no listener for it, then the default action is to print a stack
trace and exit the program.
All EventEmitters emit the event `newListener` when new listeners are
added. EventEmitters also emit the event `removeListener` when listeners are
removed, and `removeListenerAny` when listeners added through `onAny` are
removed.
**Namespaces** with **Wildcards**
To use namespaces/wildcards, pass the `wildcard` option into the EventEmitter
constructor. When namespaces/wildcards are enabled, events can either be
strings (`foo.bar`) separated by a delimiter or arrays (`['foo', 'bar']`). The
delimiter is also configurable as a constructor option.
An event name passed to any event emitter method can contain a wild card (the
`*` character). If the event name is a string, a wildcard may appear as `foo.*`.
If the event name is an array, the wildcard may appear as `['foo', '*']`.
If either of the above described events were passed to the `on` method,
subsequent emits such as the following would be observed...
```javascript
emitter.emit('foo.bazz');
emitter.emit(['foo', 'bar']);
```
# Multi-level Wildcards
A double wildcard (the string `**`) matches any number of levels (zero or more) of events. So if for example `'foo.**'` is passed to the `on` method, the following events would be observed:
````javascript
emitter.emit('foo');
emitter.emit('foo.bar');
emitter.emit('foo.bar.baz');
````
On the other hand, if the single-wildcard event name was passed to the on method, the callback would only observe the second of these events.
### emitter.addListener(event, listener)
### emitter.on(event, listener)
Adds a listener to the end of the listeners array for the specified event.
```javascript
server.on('data', function(value1, value2, value3, ...) {
console.log('The event was raised!');
});
```
```javascript
server.on('data', function(value) {
console.log('The event was raised!');
});
```
### emitter.onAny(listener)
Adds a listener that will be fired when any event is emitted. The event name is passed as the first argument to the callback.
```javascript
server.onAny(function(event, value) {
console.log('All events trigger this.');
});
```
### emitter.offAny(listener)
Removes the listener that will be fired when any event is emitted.
```javascript
server.offAny(function(value) {
console.log('The event was raised!');
});
```
#### emitter.once(event, listener)
Adds a **one time** listener for the event. The listener is invoked
only the first time the event is fired, after which it is removed.
```javascript
server.once('get', function (value) {
console.log('Ah, we have our first value!');
});
```
### emitter.many(event, timesToListen, listener)
Adds a listener that will execute **n times** for the event before being
removed. The listener is invoked only the first **n times** the event is
fired, after which it is removed.
```javascript
server.many('get', 4, function (value) {
console.log('This event will be listened to exactly four times.');
});
```
### emitter.removeListener(event, listener)
### emitter.off(event, listener)
Remove a listener from the listener array for the specified event.
**Caution**: Calling this method changes the array indices in the listener array behind the listener.
```javascript
var callback = function(value) {
console.log('someone connected!');
};
server.on('get', callback);
// ...
server.removeListener('get', callback);
```
### emitter.removeAllListeners([event])
Removes all listeners, or those of the specified event.
### emitter.setMaxListeners(n)
By default EventEmitters will print a warning if more than 10 listeners
are added to it. This is a useful default which helps finding memory leaks.
Obviously not all Emitters should be limited to 10. This function allows
that to be increased. Set to zero for unlimited.
### emitter.listeners(event)
Returns an array of listeners for the specified event. This array can be
manipulated, e.g. to remove listeners.
```javascript
server.on('get', function(value) {
console.log('someone connected!');
});
console.log(server.listeners('get')); // [ [Function] ]
```
### emitter.listenersAny()
Returns an array of listeners that are listening for any event that is
specified. This array can be manipulated, e.g. to remove listeners.
```javascript
server.onAny(function(value) {
console.log('someone connected!');
});
console.log(server.listenersAny()[0]); // [ [Function] ]
```
### emitter.emit(event, [arg1], [arg2], [...])
Execute each of the listeners that may be listening for the specified event
name in order with the list of arguments.
### emitter.emitAsync(event, [arg1], [arg2], [...])
Return the results of the listeners via [Promise.all](https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Promise/all).
Only this method doesn't work [IE](http://caniuse.com/#search=promise).
```javascript
emitter.on('get',function(i) {
return new Promise(function(resolve){
setTimeout(function(){
resolve(i+3);
},50);
});
});
emitter.on('get',function(i) {
return new Promise(function(resolve){
resolve(i+2)
});
});
emitter.on('get',function(i) {
return Promise.resolve(i+1);
});
emitter.on('get',function(i) {
return i+0;
});
emitter.on('get',function(i) {
// noop
});
emitter.emitAsync('get',0)
.then(function(results){
console.log(results); // [3,2,1,0,undefined]
});
```
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