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Simple EventEmitter for your FE(mb BE)

How to install

npm install -S isemitter

bower install -S is-emitter

What for?

It's a simple implementation of event emitter that helps you to implement observers in your application. This implementation also provides an ability to classify events and split them by several groups.

Lets go:

new EventEmitter()

EventEmitter - provides event-driven system

Example:

 var settings = {
  maxListeners: 10, //10 listeners by default
  async: false, //sync mode by default
  logger: console.warn.bind(console) //console warn by default
 };

 var emitter = new EventEmitter(settings);

eventEmitter.on(eventNameList, handler)

eventEmitter.addEventListener(eventNameList, handler)

Method provide ability to subscribe on some event(s) by name and react on it(them) by handler

Kind: instance method of EventEmitter

Param Type
eventNameList string | Array
handler function

Examples:

 var emitter = new EventEmitter();

 //register event
 emitter.on('event1', function (a, b) {
  console.log(this.event + ' : a + b: ' + (a + b));
 });

 //register several events
 emitter.on(['event2', 'event3'], function (a, b) {
  console.log(this.event + ' : a + b: ' + (a + b));
 });

 emitter.emit('event1', 1, 2);
 //result: 'event1 : a + b: 3'

 emitter.emit('event2', 4, 5);
 //result: 'event2 : a + b: 9'

 //register event that is specially defined by using group name
 emitter.on('event4.somegroup', function () {
  console.log(this.event + '.' +  this.group + 'was emitted');
 });

 emitter.emit('event4');
 //result: 'event4.somegroup was emitted'

 //register group of event + classified them by using diff group names
 emitter.on(['event2.group1', 'event3.group2'], function (a, b) {
   console.log(this.event);
 });

 emitter.emit('event2');
 //result: 'event2'

 emitter.emit('event3');
 //result: 'event3'

eventEmitter.off(eventNameList, [handler])

eventEmitter.removeEventListener(eventNameList, [handler])

Method allows to remove events from eventEmitter by eventName, eventName.group, .group, eventNameList

Kind: instance method of EventEmitter

Param Type
evenNameList string | Array
[handler] function

Examples:

var emitter = new EventEmitter();

emitter.on(['event1', 'event2'], function () {
 console.log('event1 or event2');
});

//you can get rid of these events by using of in this way
emitter.off('event1');
emitter.off('event2');

//or this way
emitter.off(['event1', 'event2']);

//Register classified events
emitter.on(['e1.group1', 'e2.group1', 'e3.group2', 'e4'], function () {
 console.log(this.event);
});

//Remove all events with .group1 classifier
emitter.off('.group1');

//Remove all events with .group2 and e4
emitter.off(['.group2', 'e4']);

emitter.on('e1.class1', function () { console.log('Hello World 1'); });
emitter.on('e1.class1', function () { console.log('Hello World 2'); });
emitter.on('e1', function () { console.log('hello world 3'); });

emitter.emit('e1');
//'Hello World 1'
//'Hello World 2'
//'hello world 3'

emitter.off('e1.class1');
emitter.emit('e1');
//'hello world 3'

eventEmitter.once(eventNameList, handler)

Methods allows you to subscribe on some event(s) and remove subscription automatically after event(s) will happen (one time)

Kind: instance method of EventEmitter

Param Type
eventNameList string | Array
handler function

Example:

var eventEmitter = new EventEmitter();
var counter = 0;

eventEmitter.once('event', function () {
 counter++;
});

eventEmitter.emit('event');
eventEmitter.emit('event');
eventEmitter.emit('event');

console.log(counter); // => 1

eventEmitter.many(eventNameList, handler, times)

Methods allows you to subscribe on some event(s) and remove subscription automatically after event(s) will happen (several times)

Kind: instance method of EventEmitter

Param Type
eventNameList string | Array
handler function
times number

Example:

var eventEmitter = new EventEmitter();
var counter = 0;

eventEmitter.many('event', function () {
 counter++;
}, 2);

eventEmitter.emit('event');
eventEmitter.emit('event');
eventEmitter.emit('event');
eventEmitter.emit('event');

console.log(counter); // => 2

eventEmitter.emit(eventName, argumentsList)

eventEmitter.trigger(eventName, argumentsList)

Method allows to trigger all handler which are subscribed on some event and also pass any number of arguments

Kind: instance method of EventEmitter

Param Type Description
eventName string
argumentsList arguments of arguments

Example Sync and Async mode:

//sync mode example
var ee = new EventEmitter();

ee.on('event', function () {
 console.log('hello world sync');
});

(function () {
 ee.emit('event');
 console.log('after hello world');
})();
//'hello world sync'
//'after hello world'

ee = null;
//////////////////////////////////////////////////////////////////////////////
//async mode example
var ee = new EventEmitter({async: true});

ee.on('event', function () {
  console.log('hello world async');
});

(function () {
 ee.emit('emit');
 console.log('hello world here but happens before emit result');
})();
//'hello world here but happens before emit result'
//'hello world async'

eventEmitter.hasGroup(eventNameList, handler)

Method allows you to check whether specific group is registered

var ee = new EventEmitter();
...
...
...

ee.hasGroup('groupName'); // => true if group exists, otherwise - false

eventEmitter.hasGroup(eventNameList, handler)

Method allows you to check whether specific event is registered

var ee = new EventEmitter();
...
...
...

ee.hasEvent('eventName'); // => true if group exists, otherwise - false

eventEmitter.before(eventNameList, [handler])

eventEmitter.offBefore(eventNameList, [handler])

Method helps you to register handler(s) which will be invoked before all registered (via .on) event handlers Inside it uses EventEmitter instance to register "before" action. ".before" it just sugar and you can compare it to .on method, but you should be aware that all events which will be registred via method .before will be invoked only if you have events registered via method .on

var ee = new EventEmitter();

ee.on('event1', someHandler1);
ee.on('event2', someHandler2);
ee.on('event3', someHandler3);

// You can use event name or list with event names and use groups of course to simplify process of deletion
ee.before('event1.g1', beforeHandler);
ee.before(['event2.g1', 'event3.g2'], beforeHandler2);

ee.emit('event1');
// beforeHandler() -> someHandler1()

ee.emit('event3');
// beforeHandler2() -> someHandler3()

ee.offBefore('.g1');

ee.emit('event1');
// someHandler1();
...

eventEmitter.after(eventNameList, [handler])

eventEmitter.offAfter(eventNameList, [handler])

Method helps you to register handler(s) which will be invoked after all registered (via .on) event handlers Inside it uses EventEmitter instance to register "after" actions. ".after" it just sugar and you can compare it to .on method, but you should be aware that all events which will be registred via method .after will be invoked only if you have events registered via method .on

var ee = new EventEmitter();

ee.on('event1', someHandler1);
ee.on('event2', someHandler2);
ee.on('event3', someHandler3);

// You can use event name or list with event names and use groups of course to simplify process of deletion
ee.after('event1.g1', afterHandler);
ee.after(['event2.g1', 'event3.g2'], afterHandler2);

ee.emit('event1');
// someHandler1() -> afterHandler()

ee.emit('event3');
// someHandler3() -> afterHandler2()

ee.offAfter('.g1');
...

eventEmitter.group(groupName)

Method allows to create a simple helper to register and unregister events for specific group

Example

var ee = new EventEmitter();

var someGroup = ee.group('some-group');

someGroup.on('event', function () {
 console.log('handler of some-group event');
});

someGroup.on('event1', function () {
 console.log('handler of some-group event1');
});

ee.emit('event1');
//result -> 'handler of some-group event1'

someGroup.off('event'); //remove handlers for 'event' for some-group
//also possible cases:
// someGroup.off() -> remove all events
// someGroup.off(['event', 'event1']); // remove events by name

eventEmitter.getMaxListeners()

Method allows to get max listeners count

Kind: instance method of EventEmitter
Returns: number - Returns max listeners count

eventEmitter.setMaxListeners(number)

Method allows to set max listeners count

Kind: instance method of EventEmitter

Param Type Description
number number of max listeners count

this inside event handler

Explanation:

var ee = new EventEmitter();

ee.on('event', function () {
 this.event; //event -> string (name of event)
 this.group; //group -> string (name of group)
 this.stop; //stop -> function (method stops event propagation to other handlers)
});

Stop Example:

var ee = new EventEmitter();

var counter = 1;
var handler = function () {
 console.log('Counter:HELLO');
 if(counter > 2) {
  counter = 1;
  this.stop();
 }
 counter++;
};

ee.on('event', handler);
ee.on('event', handler);
ee.on('event', handler);
ee.on('event', handler);
ee.on('event', handler);
ee.on('event', handler);

ee.emit('event'); // => results:
//'Counter:HELLO'
//'Counter:HELLO'

ee.emit('event'); // => results:
//'Counter:HELLO'
//'Counter:HELLO'

ee.off('event');

Angular Example

(function (ng, EventEmitter) {
 'use strict';
 ng.module('yourAppModule')
  .factory('EventEmitterFactory', EventEmitterFactory)
  .factory('GlobalEventEmitter', GlobalEventEmitter)
  .factory('SomeServiceOfYourApp', SomeServiceOfYourApp)
  .directive('someDirective', someDirective);

 function EventEmitterFactory() {
  return {
   create: function (settings) {
    return new EventEmitter(settings);
   }
  };
 }

 function GlobalEventEmitter(emitterFactory) {
  return emitterFactory.create();
 }

 //using with other services

 SomeServiceOfYourApp.$inject = ['GlobalEventEmitter'];
 function SomeServiceOfYourApp (emitter) {
  var state = null;

  return {
   setState: function (currState) {
    state = currState;
    emitter.emit('STATE_CHANGE', state);
   },

   onStateChange: function (componentName, handler) {
    //using group to mark registred handlers for component
    emitter.on('STATE_CHANGE.' + componentName, handler);
   };

   offStateChange: function (componentName) {
    //using remove event handler according to the specific group
    emitter.off('.' + componentName);
   };
  };
 }

 someDirective.$inject = ['SomeServiceOfYourApp'];
 function someDirective(someService) {
  return  {
   restrict: 'EA',
   link: function (scope) {
    someService.onStateChange('myDirectiveName', function () {
     console.log('hello world');
    });

    someService.onStateChange('myDirectiveName', function () {
     console.log('hello world 2');
    });

    scope.$on('$destroy', function () {
     //remove all handlers for this component
     someService.offStateChange('myDirectiveName');
    });
   }
  }
 }

})(angular, EventEmitter);

Use jsbin to see the example of using EventEmitter with angular routes

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Full-fledged event emitter with naming group support

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