event-emitter

Environment agnostic event emitter

Installation

$ npm install event-emitter

To port it to Browser or any other (non CJS) environment, use your favorite CJS bundler. No favorite yet? Try: Browserify, Webmake or Webpack

Usage

1var ee = require('event-emitter');
2
3var MyClass = function () { /* .. */ };
4ee(MyClass.prototype); // All instances of MyClass will expose event-emitter interface
5
6var emitter = new MyClass(), listener;
7
8emitter.on('test', listener = function (args) {
9  // … react to 'test' event
10});
11
12emitter.once('test', function (args) {
13  // … react to first 'test' event (invoked only once!)
14});
15
16emitter.emit('test', arg1, arg2/*…args*/); // Two above listeners invoked
17emitter.emit('test', arg1, arg2/*…args*/); // Only first listener invoked
18
19emitter.off('test', listener);              // Removed first listener
20emitter.emit('test', arg1, arg2/*…args*/); // No listeners invoked

Additional utilities

allOff(obj) (event-emitter/all-off)

Removes all listeners from given event emitter object

hasListeners(obj[, name]) (event-emitter/has-listeners)

Whether object has some listeners attached to the object. When name is provided, it checks listeners for specific event name

1var emitter = ee();
2var hasListeners = require('event-emitter/has-listeners');
3var listener = function () {};
4
5hasListeners(emitter); // false
6
7emitter.on('foo', listener);
8hasListeners(emitter); // true
9hasListeners(emitter, 'foo'); // true
10hasListeners(emitter, 'bar'); // false
11
12emitter.off('foo', listener);
13hasListeners(emitter, 'foo'); // false

pipe(source, target[, emitMethodName]) (event-emitter/pipe)

Pipes all events from source emitter onto target emitter (all events from source emitter will be emitted also on target emitter, but not other way).
Returns pipe object which exposes pipe.close function. Invoke it to close configured pipe.
It works internally by redefinition of emit method, if in your interface this method is referenced differently, provide its name (or symbol) with third argument.

unify(emitter1, emitter2) (event-emitter/unify)

Unifies event handling for two objects. Events emitted on emitter1 would be also emitted on emitter2, and other way back.
Non reversible.

1var eeUnify = require('event-emitter/unify');
2
3var emitter1 = ee(), listener1, listener3;
4var emitter2 = ee(), listener2, listener4;
5
6emitter1.on('test', listener1 = function () { });
7emitter2.on('test', listener2 = function () { });
8
9emitter1.emit('test'); // Invoked listener1
10emitter2.emit('test'); // Invoked listener2
11
12var unify = eeUnify(emitter1, emitter2);
13
14emitter1.emit('test'); // Invoked listener1 and listener2
15emitter2.emit('test'); // Invoked listener1 and listener2
16
17emitter1.on('test', listener3 = function () { });
18emitter2.on('test', listener4 = function () { });
19
20emitter1.emit('test'); // Invoked listener1, listener2, listener3 and listener4
21emitter2.emit('test'); // Invoked listener1, listener2, listener3 and listener4

Tests

$ npm test