It triggers an event to which anyone can listen. Different libraries offer different implementations and for different purposes, but the basic idea is to provide a framework for issuing events and subscribing to them.

Example from jQuery:

// Subscribe to event.

$('#foo').bind('click', function() {

    alert(Click!);

});



// Emit event.

$('#foo').trigger('click');

However, with jQuery in order to emit an event you need to have a DOM object, and cannot emit events from an arbitrary object. This is where event-emitter becomes useful. Here's some pseudo-code to demo custom events (the exact same pattern as above):

// Create custom object which inherits from emitter. Keyword extend is just a pseudo-code.

var myCustomObject = {};

extend(myCustomObject , EventEmitter);



// Subscribe to event.

myCustomObject.on(somethingHappened, function() { 

    alert(something happened!);

});



// Emit event.

myCustomObject.emit(somethingHappened);