From a6c3d7121b249867e8eaf9c6069ea5ab3cbd942d Mon Sep 17 00:00:00 2001 From: Micheil Smith Date: Sun, 14 Nov 2010 23:51:57 +1100 Subject: [PATCH] Reworked and cleaned up documentation for Events --- doc/api/events.markdown | 86 ++++++++++++++++++++--------------------- 1 file changed, 41 insertions(+), 45 deletions(-) diff --git a/doc/api/events.markdown b/doc/api/events.markdown index e3972668d9..85715a7350 100644 --- a/doc/api/events.markdown +++ b/doc/api/events.markdown @@ -1,86 +1,82 @@ -## EventEmitter +## Events -Many objects in Node emit events: a TCP server emits an event each time -there is a stream, a child process emits an event when it exits. All -objects which emit events are instances of `events.EventEmitter`. +Many objects in Node emit events: a `net.Server` emits an event each time +a peer connects to it, a `fs.readStream` emits an event when the file is +opened. All objects which emit events are instances of `events.EventEmitter`. +You can access this module by doing: `require("events");` -Events are represented by a camel-cased string. Here are some examples: -`'connection'`, `'data'`, `'messageBegin'`. +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 be then be attached to objects, to be executed when an event is emitted. These functions are called _listeners_. -`require('events').EventEmitter` to access the `EventEmitter` class. -All EventEmitters emit the event `'newListener'` when new listeners are -added. - -When an `EventEmitter` experiences an error, the typical action is to emit an -`'error'` event. Error events are special--if there is no handler for them -they will print a stack trace and exit the program. - -### Event: 'newListener' - -`function (event, listener) { }` - -This event is emitted any time someone adds a new listener. +### events.EventEmitter -### Event: 'error' +To access the EventEmitter class, `require('events').EventEmitter`. -`function (exception) { }` +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 node. +If there is no listener for it, then the default action is to print a stack +trace and exit the program. -If an error was encountered, then this event is emitted. This event is -special - when there are no listeners to receive the error Node will -terminate execution and display the exception's stack trace. +All EventEmitters emit the event `'newListener'` when new listeners are +added. -### emitter.on(event, listener) +#### emitter.addListener(event, listener) +#### emitter.on(event, listener) Adds a listener to the end of the listeners array for the specified event. - server.on('connection', function (stream) { - console.log('someone connected!'); - }); + server.on('connection', function (stream) { + console.log('someone connected!'); + }); -### emitter.once(event, listener) +#### emitter.once(event, listener) Adds a **one time** listener for the event. The listener is invoked only the first time the event is fired, after which it is removed. - server.once('connection', function (stream) { - console.log('Ah, we have our first user!'); - }); + server.once('connection', function (stream) { + console.log('Ah, we have our first user!'); + }); -### emitter.removeListener(event, listener) +#### emitter.removeListener(event, listener) Remove 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 connected!'); + var callback = function(stream) { + console.log('someone connected!'); }; - server.on('connection', callback); + server.on('connection', callback); // ... server.removeListener('connection', callback); -### emitter.removeAllListeners(event) +#### emitter.removeAllListeners(event) Removes all listeners from the listener array for the specified event. -### emitter.listeners(event) +#### emitter.listeners(event) Returns an array of listeners for the specified event. This array can be manipulated, e.g. to remove listeners. - server.on('connection', function (stream) { - console.log('someone connected!'); - }); - console.log(util.inspect(server.listeners('connection')); - // [ [Function] ] + server.on('connection', function (stream) { + console.log('someone connected!'); + }); + console.log(util.inspect(server.listeners('connection')); // [ [Function] ] - -### emitter.emit(event, [arg1], [arg2], [...]) +#### emitter.emit(event, [arg1], [arg2], [...]) Execute each of the listeners in order with the supplied arguments. + +#### Event: 'newListener' + +`function (event, listener) { }` + +This event is emitted any time someone adds a new listener.