Unhandled 'error' event

[DmitryAstafyev]

• Version: 8.6.0
• Platform: darwin
• Subsystem:

I'm not sure is a "feature" or "bug", but use case is messy.

const EventEmitter  = require('events').EventEmitter;
const Spawn = require('child_process').spawn;
const EVENTS = {
    ERROR: 'error'
};
class Service extends EventEmitter{

    run(){
        let _spawn = Spawn('badcommand', []).on('error', (error) => {
            console.log(error);
        });
    }
}

(new Service()).run();

Expected result: exit code 0 because error event is handled.

But I want to trigger "my" event also:

const EventEmitter  = require('events').EventEmitter;
const Spawn = require('child_process').spawn;
const EVENTS = {
    ERROR: 'error'
};
class Service extends EventEmitter{

    run(){
        let _spawn = Spawn('badcommand', []).on('error', (error) => {
            this.emit(EVENTS.ERROR, error); //<--- Here I want to trigger error event of my service
        });
    }
}

(new Service()).run();

But now result is: exit code 1 - application is crashed within Unhandled 'error' event

Simple changing of event's name fix it:

const EventEmitter  = require('events').EventEmitter;
const Spawn = require('child_process').spawn;
const EVENTS = {
    ERROR: 'error'
};
class Service extends EventEmitter{

    run(){
        let _spawn = Spawn('badcommand', []).on('error', (error) => {
            this.emit('ServiceError', error); //<--- Here I want to trigger error event of my service
        });
    }
}

(new Service()).run();

And again I have exit code 0 as it should be.

So, is a bug? Or feature? Why I cannot use same naming for events even I don't inherite from spawn.

If it's some kind of specific it would be great to have some more informative logs in console for such cases.

Thanks.

[addaleax]

There is no error handler on your Service instance, but you’re emitting an error on it, so I would say this is expected behavior and not a bug in Node.

If it's some kind of specific it would be great to have some more informative logs in console for such cases.

Could you give a suggestion of output that you would have found helpful?

Also, I’d suggest moving this discussion to https://github.com/nodejs/help/, I think that’s a better place for it (because it’s not a bug with Node).

[DmitryAstafyev]

Many thanks for so quick response.
Regarding information. I don't know. I added handler for error event to spawn. And expect that this is enough to be sure, that application will not be exit 1. "My" event error I would like to trigger also, but I don't what to make a user of service listen it. User can listen error event or not.
Maybe, I don't know: something like handler of "error" event is ignored, because... Unhandled 'error' event. Just to find quickly what is a reason.

[addaleax]

handler of "error" event is ignored

How would Node know how the error handler on another object relates to the one on your own class?

[DmitryAstafyev]

That's why I'm asking. The simplest thing for me, it's just do not use same naming of events.
And here a "why" I didn't want to make developer listen error (to leave two ways catch it: within reject and within error event):

const EventEmitter  = require('events').EventEmitter;
const Spawn = require('child_process').spawn;
const EVENTS = {
    ERROR: 'error'
};
class Service extends EventEmitter {

    run(){
        return new Promise((resolve, reject) => {
            let _spawn = Spawn('bad', []).on('error', (error) => {
                console.log('"original error"');
                reject();
                this.emit('error', error);
            });
        });
    }
}
const service = new Service();
service.run().catch((error)=>{
    console.log(error);
});

One again thanks for your response.