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87 lines
2.5 KiB
87 lines
2.5 KiB
14 years ago
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## EventEmitter
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Many objects in Node emit events: a TCP server emits an event each time
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there is a stream, a child process emits an event when it exits. All
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objects which emit events are instances of `events.EventEmitter`.
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Events are represented by a camel-cased string. Here are some examples:
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`'connection'`, `'data'`, `'messageBegin'`.
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Functions can be then be attached to objects, to be executed when an event
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is emitted. These functions are called _listeners_.
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`require('events').EventEmitter` to access the `EventEmitter` class.
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All EventEmitters emit the event `'newListener'` when new listeners are
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added.
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When an `EventEmitter` experiences an error, the typical action is to emit an
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`'error'` event. Error events are special--if there is no handler for them
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they will print a stack trace and exit the program.
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### Event: 'newListener'
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`function (event, listener) { }`
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This event is emitted any time someone adds a new listener.
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### Event: 'error'
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`function (exception) { }`
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If an error was encountered, then this event is emitted. This event is
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special - when there are no listeners to receive the error Node will
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terminate execution and display the exception's stack trace.
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### emitter.on(event, listener)
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Adds a listener to the end of the listeners array for the specified event.
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server.on('connection', function (stream) {
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console.log('someone connected!');
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});
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### emitter.once(event, listener)
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Adds a **one time** listener for the event. The listener is
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invoked only the first time the event is fired, after which
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it is removed.
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server.once('connection', function (stream) {
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console.log('Ah, we have our first user!');
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});
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### emitter.removeListener(event, listener)
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Remove a listener from the listener array for the specified event.
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**Caution**: changes array indices in the listener array behind the listener.
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var callback = function(stream) {
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console.log('someone connected!');
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};
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server.on('connection', callback);
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// ...
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server.removeListener('connection', callback);
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### emitter.removeAllListeners(event)
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Removes all listeners from the listener array for the specified event.
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### emitter.listeners(event)
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Returns an array of listeners for the specified event. This array can be
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manipulated, e.g. to remove listeners.
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server.on('connection', function (stream) {
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console.log('someone connected!');
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});
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console.log(util.inspect(server.listeners('connection'));
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// [ [Function] ]
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### emitter.emit(event, [arg1], [arg2], [...])
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Execute each of the listeners in order with the supplied arguments.
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