Event handler for 'error'

[drmrbrewer]

The example given for the error event is as follows:

const queue = new PQueue({concurrency: 2});
queue.on('error', error => {
    console.error(error);
});
queue.add(() => Promise.reject(new Error('error')));

But as noted here:

If your items can potentially throw an exception, you must handle those errors from the returned Promise or they may be reported as an unhandled Promise rejection and potentially cause your process to exit immediately.

The error event handler example above doesn't follow this guidance, and throws an exception that isn't handled, crashing the node app, so that the event handler is sadly never called.

So we must add an error handler on the item to catch the error... but in which case what use does the error event handler have?

[rijkvanzanten]

@drmrbrewer just ran into the same thing. I ended up adding an empty catch to the queue.add() in order to have the event handler take care of the error handling:

const queue = new PQueue({concurrency: 2});

queue.on('error', error => {
    console.error(error);
});

queue.add(() => Promise.reject(new Error('error'))).catch(() => { /* handled in event callback */ });