node.js处理未设置的错误事件

Question

I'm working on a module that emits events, one of which is an 'error' event.

For example:

function A() {}

function A.prototype.start() {
 var error = true;
 if (error) {
  this.emit('error', error);
 }
 return this;
}

var a = new A()
a.on('error', function(err) {})

What happens is that even though I'm listening to the error event, the event is emitted, I guess before the listener is registered or the return of this . What I've done is wrapped the emit in a setImmediate , such as:

function A.prototype.start() {
 var error = true;
 if (error) {
  setImmediate(function() {
   this.emit('error', error);
  });
 }
 return this;
}

As a general practice, is this fine? or would there be a better way that's recommended for handling this and similar situations.

Answer 1

It's good solution.

EventEmitter events are pure-JS and don't get scheduled on the event loop; they are delivered synchronously.

In your situation, you emit an event before there's a listener, because you add a listener only after the event has been emitted. If you "wait" for the next round of the event loop, by using setImmediate() , you basically postpone emitting the event until a time when the listener has been added.