javascript - 尽管未显式调用事件处理程序，但为什么会触发 eventemitter

Question

以下代码来自http://www.tutorialspoint.com/nodejs/nodejs_event_loop.htm 。在该代码中，data_received 事件在 connectHandler() 函数的定义中被触发。尽管未调用 connectHandler() 函数，但会触发 data_received 事件。这怎么可能？

// Import events module
var events = require('events');
// Create an eventEmitter object
var eventEmitter = new events.EventEmitter();

// Create an event handler as follows
var connectHandler = function connected() {
   console.log('connection succesful.');

   // Fire the data_received event 
   eventEmitter.emit('data_received');
}

// Bind the connection event with the handler
eventEmitter.on('connection', connectHandler);

// Bind the data_received event with the anonymous function
eventEmitter.on('data_received', function(){
   console.log('data received succesfully.');
});

// Fire the connection event 
eventEmitter.emit('connection');

console.log("Program Ended.");

输出:

connection succesful.
data received succesfully.
Program Ended.

Answer 1

// Fire the connection event 
eventEmitter.emit('connection');

在这里，您应该观察到正在触发一个“连接”事件，该事件绑定(bind)到 connectHandler 函数，从而调用更多事件。