event loop model in javascript

Question

based on: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/EventLoop

stack frame is empty before next event is processed. So why in folowing snippet alert displays 1 instead of 0 because alert function should run before callback

var a=0;
var b={};

$(b).on("event", function (){
  a++;
});

$(b).trigger("event");
alert(a);

http://jsfiddle.net/nxjhokL0/

Thanks!

@NaeemShaikh Yes, it does. Just because it *sometimes* inserts it for you, doesn't mean it's okay to drop it. — Madara's Ghost, Dec 15 '14 at 12:30
@JLRishe That's not just jQuery, it reproduces with plain DOM events. — Benjamin Gruenbaum, Dec 15 '14 at 12:33
It looks like the MDN is simply a little wrong : events not involving anything outside JS might be synchronous. Which feels very wrong :( — Denys Séguret, Dec 15 '14 at 12:34
@SecondRikudo: strictly speaking, line-ending `;` characters are optional (from the point of view of the author, not the the interpreter). It just leads to horrible, horrible problems when they're automagically inserted by the interpreter (which often inserts them in unexpected, or *unanticipated*, places). — David Thomas, Dec 15 '14 at 12:34

score 3 · Accepted Answer · edited May 23 '17 at 12:05

3

Let's ignore the fact you have jQuery events here and not native DOM events since this reproduces with native DOM Events as dystroy has shown in his comment to the question.

Simply put MDN is misleading here. In general that article could use technical review.

If we check the DOM Events specification itself:

Events may be dispatched either synchronously or asynchronously.

"stack frame is empty before next event is processed. " is incorrect in the general case. It only happens with asynchronous events.

edited May 23 '17 at 12:05

Community

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answered Dec 15 '14 at 12:35

Benjamin Gruenbaum

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I'm sorry, I'm genuinely not trying to be a nuisance; I'll stop now :-/ – David Thomas Dec 15 '14 at 12:40
2

You really don't have to stop - I'm all for improving answers and your help is appreciated. In fact I don't think people do that enough around here. – Benjamin Gruenbaum Dec 15 '14 at 12:41

event loop model in javascript

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