nodejs EventEmitter

Many objects in Node emit events: a

net.Server

emits an event each timea peer connects to it, a

fs.readStream

emits an event when the file isopened. 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 eventis emitted. These functions are called
listeners. Inside a listenerfunction,

this

refers to the

EventEmitter

that the listener wasattached to.

Class: events.EventEmitter#

To access the EventEmitter class,

require('events').EventEmitter

.

When an

EventEmitter

instance experiences an error, the typical action isto 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 stacktrace and exit the program.

All EventEmitters emit the event

'newListener'

when new listeners areadded and

'removeListener'

when a listener is removed.

emitter.addListener(event, listener)#

emitter.on(event, listener)#

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. Multiplecalls passing the same combination of

event

and

listener

will result in the

listener

being added multiple times.

server.on('connection', function (stream) {
  console.log('someone connected!');
});

Returns emitter, so calls can be chained.

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

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

Returns

true

if event had listeners,

false

otherwise.

例子：

var EventEmitter = require('events').EventEmitter;
var event = new EventEmitter();

event.on('some_event', function(who, opcode, opobject){
        console.log("listener 1 response to some_event");
        console.log("%s %s %s\n", who, opcode, opobject);                                                                                                                                                    
});

event.on('some_event', function(){
        console.log("listener 2 response to some_event");
});

setTimeout(function(){
        event.emit('some_event', "xiaoming", "eat", "rice");
}, 1000);

结果输出：

listener 1 response to some_event
xiaoming eat rice

listener 2 response to some_event