node.js eventEmitter : Listen for events across files

Question

Just getting started on Node.js, I have the following query:

I have a following javascript in my server.js file:

====================================================

function onRequest(request, response) {
  var pathname = url.parse(request.url).pathname;
  route(handle, pathname, response);
  console.log("Request for " + pathname + " received.");
}

var server = http.createServer(onRequest)
server.listen(8888);
console.log("Server started")

===============================================================

I have another js file, where I want to register a listener for the "listening" event emitted by server, or for that matter any event that is emitted by server.

I cannot change the original file to export the server object.

Is there any way I can achieve my objective ?

Answer 1

You'll want to either pass the server object into your other module like below or you'll want to expose a function on your other module that you can then assign as a listener in the parent module. Either way would work. It just depends where you want the .on call to be.

// app.js

var otherModule = require('./other-module.js');

function onRequest(request, response) {

  var pathname = url.parse(request.url).pathname;
  route(handle, pathname, response);

  console.log("Request for " + pathname + " received.");
}

var server = http.createServer(onRequest);
otherModule.init(server);
server.listen(8888, function () {
  console.log("Server started");
}); // <-- Passing in this callback is a shortcut for defining an event listener for the "listen" event.

---

// other-module.js

exports.init = function (server) {
  server.on('listen', function () {
    console.log("listen event fired.");
  });
};

In the above example I setup two event listeners for the listen event. The first one is registered when we pass in a callback function to server.listen. That's just a shortcut for doing server.on('listen', ...). The second event handler is setup in other-module.js, obviously :)