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（）函数的定义中触发。虽然未调用connectHandler（）函数，但会触发data_received事件。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');

在这里你应该观察到一个'connection'事件被触发，它被绑定到connectHandler函数，从而调用更多的事件。

虽然事件处理程序未被显式调用，但为什么会发出eventemitter

1 个答案: