Multiple callback problem

[NamTThai]

Here is a snippet of me using node-imap

      imap.once('ready', function() {
        imap.openBox(mailboxName, true, function(error, box) {
          if (error) {
            return callback(error);
          }

          imap.search(searchArray, function(error, results) {
            if (error) {
              return callback(error);
            }

            var result = {};
            var f = imap.fetch(results, {
              envelope: true,
              bodies: 'TEXT'
            });

            f.on('message', function(msg, seqno) {
              result[seqno] = {};
              msg.on('body', function(stream, info) {
                var buffer = "";
                stream.on('data', function(chunk) {
                  buffer += chunk;
                });
                stream.once('end', function() {
                  result[seqno].body = buffer;
                });
              });
              msg.once('attributes', function(attrs) {
                result[seqno].attributes = attrs;
              });
            });

            f.once('error', function(error) {
              return callback(error);
            });

            f.once('end', function() {
              imap.end();
              return callback(null, result);
            });
          });
        });
      });

      imap.once('error', function(error) {
        return callback(error);
      });

      imap.connect();

Occasionally when error occurs, I get multiple callback problem: the function callback is supposed to be called only once. My expectation is that when an error occurs, callback triggers and imap just stop doing everything else. But apparently, some later events still trigger, and my callback function gets called again.

Which one is it?

Is it the ImapFetch#end event? Does it get called even after an error occur?

[mscdex]

end will get emitted no matter what, so that is most likely what you're seeing.

[NamTThai]

Is there any alternatives to end that will emit after message but not when error occurs? Like jQuery ajax success event

[mscdex]

Not currently, no.