Events

Many objects in Ruff emit events.
All objects which emit events are instances of events.EventEmitter.
You can access this module by doing: require("events");

Typically, event names are represented by a camel-cased string, however,
there aren’t any strict restrictions on that, as any string will be accepted.

Functions can then be attached to objects, to be executed when an event
is emitted. These functions are called listeners. Inside a listener
function, this refers to the EventEmitter that the listener was
attached to.

Class: events.EventEmitter

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Use require('events') to access the EventEmitter class.

var EventEmitter = require('events');

When an EventEmitter instance experiences an error, the typical action is
to emit an 'error' event. Error events are treated as a special case in
Ruff. 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 and 'removeListener' when a listener is removed.

emitter.addListener(event, listener)

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

emitter.on(event, listener)

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Adds a listener to the end of the listeners array for the specified event.
No checks are made to see if the listener has already been added. Multiple
calls passing the same combination of event and listener will result in the
listener being added multiple times.

//TODO fs has not been achieved
fs.readlink('path', function (stream) {
  console.log('someone read!');
});

Returns emitter, so calls can be chained.

emitter.once(event, listener)

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Adds a one time listener for the event. This listener is
invoked only the next time the event is fired, after which
it is removed.

//TODO fs has not been achieved
fs.once('readlink', function (stream) {
  console.log('Ah, we have our first user!');
});

Returns emitter, so calls can be chained.

emitter.removeListener(event, listener)

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Removes a listener from the listener array for the specified event.
Caution: changes array indices in the listener array behind the listener.

var callback = function(stream) {
  console.log('someone read!');
};
fs.on('readlink', callback);
// ...
fs.removeListener('readlink', callback);

removeListener will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified event, then removeListener must be called
multiple times to remove each instance.

Returns emitter, so calls can be chained.

emitter.removeAllListeners([event])

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Removes all listeners, or those of the specified event. It’s not a good idea to
remove listeners that were added elsewhere in the code, especially when it’s on
an emitter that you didn’t create (e.g. file streams).

Returns emitter, so calls can be chained.

emitter.setMaxListeners(n)

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

By default EventEmitters will print a warning if more than 10 listeners are
added for a particular event. 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 Infinity (or 0) for unlimited.

Returns emitter, so calls can be chained.

emitter.getMaxListeners()

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Returns the current max listener value for the emitter which is either set by
emitter.setMaxListeners(n) or defaults to EventEmitter.defaultMaxListeners.

This can be useful to increment/decrement max listeners to avoid the warning
while not being irresponsible and setting a too big number.

emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', function () {
  // do stuff
  emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});

EventEmitter.defaultMaxListeners

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

emitter.setMaxListeners(n) sets the maximum on a per-instance basis.
This class property lets you set it for all EventEmitter instances,
current and future, effective immediately. Use with care.

Note that emitter.setMaxListeners(n) still has precedence over
EventEmitter.defaultMaxListeners.

emitter.listeners(event)

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Returns a copy of the array of listeners for the specified event.

//TODO
fs.on('readlink', function (stream) {
  console.log('someone read!');
});
console.log(util.inspect(fs.listeners('readlink'))); // [ [Function] ]

emitter.emit(event[, arg1][, arg2][, …])

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Calls each of the listeners in order with the supplied arguments.

Returns true if event had listeners, false otherwise.

emitter.listenerCount(type)

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

  • type {Value} The type of event

Returns the number of listeners listening to the type of event.

Event: ‘newListener’

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

  • event {String} The event name
  • listener {Function} The event handler function

This event is emitted before a listener is added. When this event is
triggered, the listener has not been added to the array of listeners for the
event. Any listeners added to the event name in the newListener event
callback will be added before the listener that is in the process of being
added.

Event: ‘removeListener’

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

  • event {String} The event name
  • listener {Function} The event handler function

This event is emitted after a listener is removed. When this event is
triggered, the listener has been removed from the array of listeners for the
event.

Inheriting from ‘EventEmitter’

Ruff available: v1.6.0
Ruff Lite available: v0.6.0

Inheriting from EventEmitter is no different from inheriting from any other
constructor function. For example:

'use strict';
var util = require('util');
var EventEmitter = require('events');

function MyEventEmitter() {
  // Initialize necessary properties from `EventEmitter` in this instance
  EventEmitter.call(this);
}

// Inherit functions from `EventEmitter`'s prototype
util.inherits(MyEventEmitter, EventEmitter);