如何从nodejs中的构造函数发出/捕获事件？

There are already a lot of questions, how to emit event from constructor in nodejs. Most number of this issues - event is fired before listener is added:

已经有很多问题，如何从nodejs中的构造函数发出事件。大多数问题 - 在添加侦听器之前触发事件：

var fooBar = new FooBar() // event is emitted
fooBar.on('event', function(){}); // never will be executed

There is a workaround: to fire event in constructor only after newListener event is fired. In this case, only one listener can be added. Is this normal practice to do that?

有一种解决方法：仅在触发newListener事件后才在构造函数中触发事件。在这种情况下，只能添加一个侦听器。这是正常做法吗？

I see that readline in fact provides same interface:

我看到readline实际上提供了相同的接口：

var io = readline.createInterface({
  input: process.stdin,
  terminal: false
});

io.on('line', function(line) {}); // listener is added after constructor

Does it work using newListener event?

它是否可以使用newListener事件？

1 个解决方案

#1

Here's another workaround, using setImmediate:

这是使用setImmediate的另一种解决方法：

var EventEmitter = require('events').EventEmitter;
var inherits     = require('util').inherits;

function FooBar() {
  var instance = this;
  EventEmitter.call(instance);
  setImmediate(function() {
    instance.emit('event', 'hello world');
  });
}

inherits(FooBar, EventEmitter);

var fooBar = new FooBar();
fooBar.on('event', function(value) {
  console.log('got event:', value);
});

This makes emitting the event asynchronous, which means that it will be scheduled until after any synchronous code (like calling the constructor and adding the event listener) is run.

这使得事件发生异步，这意味着它将被调度，直到运行任何同步代码（如调用构造函数和添加事件侦听器）之后。

#1