The cardiologist can't tell if my heart is beating!

Question

I have found a... strange, to say the least, error on Stack Overflow. I was just browsing normally and I decided to open the error console, and I saw this:

Uncaught TypeError: Cannot call method 'isHeartBeating' of undefined

I thought that was a bit odd, so I found the line on which the error was:

StackExchange.cardiologist.isHeartBeating()

Stack Exchange has a cardiologist? And it can't tell if my heart is beating?! Are we in a Q&A site or an inexperienced hospital?

Here is some context for that code:

case "answer-add":0==$("#answer-"+d.answerid).length&&(p.push(d.answerid),StackExchange.cardiologist.isHeartBeating()?StackExchange.helpers.DelayedReaction(k,5E3).trigger():k(),StackExchange.cardiologist.notifiedOfNewAnswer());break;

And here it is more readable:

case "answer-add":
  0 == $("#answer-"+d.answerid).length &&
    (p.push(d.answerid),
    StackExchange.cardiologist.isHeartBeating() ?
    StackExchange.helpers.DelayedReaction(k,5E3).trigger() :
    k(),StackExchange.cardiologist.notifiedOfNewAnswer());
break;

And here it is from the dev code:

function postAnswerAdd(post) {
    if ($('#answer-' + post.answerid).length != 0) return;

    answersToShow.push(post.answerid);

    if (StackExchange.cardiologist.isHeartBeating()) {
        var newAnswers = StackExchange.helpers.DelayedReaction(showNewAnswerNotification, 5000);
        newAnswers.trigger();
    } else {
        showNewAnswerNotification();
    }

    StackExchange.cardiologist.notifiedOfNewAnswer();
}

---

What is this strange error?

(note: it is on line 18 of https://cdn.sstatic.net/js/full.js?v=2cb347042411)

Answer 1

EDIT: This question is about a bug that was fixed about about 2.5 years ago (per Adam Lear), despite this question not appearing to have any submitted answers until now.

Stack Exchange has a cardiologist?

Yes, actually, in a way. There has been a background object called "StackExchange.cardiologist".

And it can't tell if my heart is beating?!

More precisely, the error you found means that the cardiologist cannot be found, not that the cardiologist can't tell if a heart is beating. And the "heartbeat" being referenced is background communication between the StackExchange page in your browser and a StackExchange server. "Heartbeat" is a bit of a misnomer for such meaningful communication. But still, the communication is periodic (it happens regularly), just like a real animal's heartbeat.

Are we in a Q&A site or an inexperienced hospital?

Haha -- But all jokes aside, a Q&A site. A Q&A site with back-end programmers who come up with all kinds of names for the parameters and objects that are usually entirely behind-the-scenes.

What is this strange error? ["Uncaught TypeError: Cannot call method 'isHeartBeating' of undefined"]

Beyond what was referenced above -- that there is code that cannot call the method 'isHeartBeating' because it doesn't have a valid connection or reference to a 'cardiologist' object -- beyond that, it's nothing to be too concerned about unless you're noticing problems in front-end functionality, like difficulty reading or posting a question, answer, or comment. (And you haven't mentioned any such difficulty.) Yes, it's a bug, and it's good to report such things, but it's more of a curiosity than a real problem based on the way the question has been phrased, no?

Reference: What is sent and received from the server during a "heartbeat" and how often does it beat? (with thanks to @balpha for providing that link in a comment)