为什么我的节点事件回调在事件中显示为undefined？

Question

I am trying to pass back a url string as "data" into my eventhandler.

My request to the server is " https://172.20.10.6/index.html ". The console.log below prints out "/index.html" as I expect.

switch(req.method) {
    case 'GET':

    console.log("logged from plugin-https.js: url: " + req.url);

     ee.emit("dataIn", req.url);

     break;

Below is the eventHandler code.
The console.log(data); evaluates to "undefined". I am trying to figure out why this is. It seems like a pretty straightforward direct callback, so I am wondering why the data is not defined when it shows up in the eventhandling code.

     plugin = rtrn;
         console.log('4');
         plugin.dataIn(config, function(err, data) {
           if(err, data) {

             console.log('error geting data');
           } else {
            // This is where request events are being handled.  
            console.log(data);



            console.log('We are in the event handling codeblock of funtion startRuntime() located in interactor.js');

Also, here is my callback code

var ee = new events.EventEmitter();

function dataIn(config, callback) {
 if(typeof callback === 'function') {

   ee.on("dataIn", callback);

Answer 1

It looks like you're swallowing errors.

if(err, data) {
    console.log('error geting data');
}

That condition (err, data) will ignore the value of err . If data is undefined, it will be falsy and you won't know that you had an error. You probably want something more like this:

if (err) {
    console.log('error getting data')
}

Tracing back to your emitter, you are emitting in a way that sends your data to the first argument, which should be where the error goes. So this:

ee.emit("dataIn", req.url);

...should be more like this:

ee.emit("dataIn", null, req.url);