事件发射器总是按照它们发射的顺序一个接一个地发射

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

var ringBell = function ringBell()                                                                                                                                                         
{                                                                                                                                                                                          
 console.log('ring ring ring');                                                                                                                                                            
}                                                                                                                                                                                          

var lockDoor = function lockDoor()                                                                                                                                                         
{                                                                                                                                                                                          
console.log("lock door");                                                                                                                                                                  
}                                                                                                                                                                                          

eventEmitter.on("ringBell", ringBell);                                                                                                                                                     
eventEmitter.on("lockDoor", lockDoor);                                                                                                                                                     
eventEmitter.emit('ringBell');                                                                                                                                                             
eventEmitter.emit('lockDoor');
var events = require('events');