How to create custom event listener in node.js (express.js)?

I have a giant function with a lot of nested callbacks. I want 开发者_如何学编程to make it cleaner and easier to handle. So, I'm thinking of using custom event listeners

Like, when a function is done, in the callback, instead of putting a chunk of code, it just emits an event, and then the listener will run.

So, how to do that in node.js? I am still looking for a good example to guide me through.

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You can set events like this

app.on('event:user_created', callback);

Then you can emit them

app.emit('event:user_created', data);

express.js uses EventEmitter.

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You probably want to create an EventEmitter object, and call emit() on it.

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I just came across this question, I'd like to chip in my 2 cents, specifically responding to Luis.

In Express, if you want the 'app' instance to listen for a custom event you would do something like:

app.on('testEvent', function () {
  return console.log('responded to testEvent');
});

app.get('/test', function (req, res) {
  app.emit('testEvent');
  return res.status(200).end();
});

Then when that route is hit, you'd see the response in the console. Of course you can implement this as you wish.

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The Node.js "events" module and the "EventEmitter" module facilitates communication between objects in Node. The EventEmitter module is at the core of Node's asynchronous event-driven architecture. Here is how you can create custom events and emit them:

const EventEmitter = require('events');
const myEmitter = new EventEmitter();

//Event Listener
const EventListenerFunc = () => {
 console.log('an event occurred!');
}

//Registering the event with the listener
myEmitter.on('eventName', EventListenerFunc);

//Emitting the event 
myEmitter.emit('eventName');