OnEmit

Event emitter that returns the event on emit [ .on() / .emit() / .emitAsync().then() ]

Take control of your events!

This is a vanilla JS event system.

As oposed to "emit-and-forget" systems, this library allows you to do stuff after all event listeners have been executed.

Usage

Include the library - it is an UMD module, works in Browser and Node.js.

var OnEmit = require('emitter');

OnEmit instance:

var emitter = new OnEmit;
 
// Add event listeners
emitter.on('anything', function (event, obj, str, num) {
   // event instanceof OnEmit.Event -> true
   // ...
   return value;
});
 
// Emit events
 
// full version
var event = emitter.emit(new OnEmit.Event('anything'), {"with": "custom arguments"}, ...);
 
// object event
emitter.emit({type: 'anything', data: ["any type"]}, ...);
// short version
emitter.emit('anything', ...);
 
console.log(event); // -> { type: "anything", timeStamp: 1453059701092, result: [return1, return2, ...] }
 
// Remove event listeners
emitter.off('anything');

As a mixin:

The OnEmit may also be used as a mixin. For example a "plain" object may become an emitter,

var user = { name: 'dima' };
OnEmit(user);
user.on('im a user', function (event){ /*...*/ })
var event = user.emit('im a user');

As a prototype mixin:

You may extend an existing prototype.

OnEmit(User.prototype);
var emitter = new User;
var event = emitter.emit('im a user as prototype method');

Bind emitter to an object

var emitter = new OnEmit;
var user = { name: 'dima' };
emitter.bind(user);
user.on(...);
var event = user.emit('im a user');

Register an event handler fn.

emitter.on(event, fn);

• event should be an event name (String), or "*" to catch all events.
• fn is an event handler of form function fn(emittedEvent, ...) { /*...*/ return value; }.
  • emittedEvent is instance of OnEmit.Event.
  • The returned value goes into emittedEvent.result[idx]. value could be a promise (used with .emitAsync()).

Register an event handler fn only once.

emitter.only(event, fn);

Register a single-shot event handler fn

removed immediately after it is invoked the first time.

emitter.once(event, fn);

Wait for event with a Promise.

emitter.when(event).then((event => {
    let { args } = event;
    // ...
}));
 
// reject after 10 seconds
emitter.when(event, 10e3).catch((error) => {
    console.log(error.type, error.message);
});

Remove event listener(s)

emitter.off(event, fn);

• Pass event and fn to remove a listener.
• Pass event to remove all listeners on that event.
• Pass nothing to remove all listeners on all events.

Emit an event with variable option args.

var event = emitter.emit(event, ...);

event argument can be either an event name (String), event properties (Object) including at least .type property, or an OnEmit.Event instance.

.emit() returns an OnEmit.Event instance, which contains an array .result of whatever event listeners have returned.

Event handlers can manipulate event properties before return.

Emit an event asynchronously.

emitter.emitAsync(event, ...).then(function (event){
    // do something after all events have fired
    console.log(event.result);
});

emitAsync uses OnEmit.setImmediate or setImmediate, if available, or setTimeout otherwise.

Emit an event after delay milliseconds.

emitter.emitAfter(delay, event, ...).then(function (event){
    // do something after all events have fired
    console.log(event.result);
});

emitAfter uses OnEmit.setTimeout or setTimeout.

Get the array of callbacks

emitter.listeners(event);

Check if this emitter has event handlers.

emitter.hasListeners(event);

Check if this OnEmit has a specific event handler fn.

emitter.hasListener(event, fn);

The special event * listens on all events.

emitter.on('*', fn);
emitter.emit('foo'); // -> fn('foo');
emitter.emit('bar'); // -> fn('bar');
emitter.off('*', fn);

License

MIT