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jquery.fn.data - get/set/changeData events syntax

in Developing jQuery Core • 12 years ago

Could someone in charge of data.js module development answer a question regarding syntax of subscribing/triggering of get/set/changeData events in case dot (.) character is present within the key argument (for example the key is "name.sub" or "name.sub.sub").

More specifically I am confused by the following blocks of code:

var parts = key.split(".");
parts[1] = parts[1] ? "." + parts[1] : "";

Here first segment after "." character is extracted, and then it is used to trigger events like this:

getData

data = this.triggerHandler("getData" + parts[1] + "!", [parts[0]]);

setData, changeData:

$this.triggerHandler( "setData" + parts[1] + "!", args );
jQuery.data( this, key, value );
$this.triggerHandler( "changeData" + parts[1] + "!", args );

First of all, I am aware of the notion of exclusive events, so the "!" character is not a part of my question.

What really bothers me is:

1. The code always uses full key to set data. But it tries to return this.data( parts[0] ) in case there is no data under the full key:

return data === undefined && parts[1] ?
this.data( parts[0] ) :
data;

It looks like inconsistency to me and I'd say it is not accurate to have such type of fallback which can lead to some unexpected behavior.

2. Again, the data is set using full key. Then why the set/get/changeData events report only first segment of the key. For example for getData:

data = this.triggerHandler("getData" + parts[1] + "!", [parts[0]]);

This behavior looks like an error to me, not just inaccuracy.

3. Also, why regardless of the number of dot-delimited segments within the key only the second one is used as a namespace for the events?

Overall, unless someone can explain the reasoning behind this behavior then for me it looks like some obscure idea to provide namespaced subscription is currently implemented in such partial/controversial way that it would be better that it were missing in code at all. Of course, maybe I am wrong, but I would definitely want to understand the meaning/intention of the code and it would be great to have the features documented.

Also, there is another very clearly defined question in this forum setData/getData events should be capable of overriding $.data()'s default behavior... but how?!? which is still unanswered and I would also hear answer to this question too.

Thanks.

Replies(5)

dave.meth..

Re: jquery.fn.data - get/set/changeData events syntax

12 years ago

Since the data events haven't been well documented, they should probably be considered experimental and may change. I agree they are not very intuitive as currently implemented.

I've created a ticket to track this: http://bugs.jquery.com/ticket/7877

algorkov

Re: Re: jquery.fn.data - get/set/changeData events syntax

12 years ago

Dave, thank you very much for your answer.

The thing I am mostly concerned about is that the implementation is not just "not very intuitive" for users of the library, but it is obvious to me that there is no clear understanding among jQuery core contributors what is currently implemented and how it should work. Please spend a minute to read on. As an evidence to this fact there are at least two statements made by jQuery team. The first one (as mentioned in the aforementioned forum post) is in jQuery 1.4.3. release notes which says that

... you can return a different value or prevent a value from being set.

But with the following lines of code we can see that the value returned by setData event handlers is not used in any way and there is no attempt to prevent the value from being set regardless of the event result:

$this.triggerHandler( "setData" + parts[1] + "!", args );
jQuery.data( this, key, value );
$this.triggerHandler( "changeData" + parts[1] + "!", args );

Also similar statement is present on John Resig's web site:

We can also override the values retrieved or set on the data method by binding to getData and setData.
Returning a value will set (or return) a completely different result.

It is clear that the intention was

to use value returned by setData handlers as actual data that should be stored under the given key
have some means to prevent value from being set depending on the event handlers execution results for the setData event.

And it is clear that it is not currently done as it is advertised in several places.

The same is true regarding data namespaces. There is following code on the same page of John Resig's presentation (highlight is mine):

$("div").bind("getData.value", function(){
return myPlugin.realValue;
});

May be I am wrong but for me it looks like an author of the code (presentation) expects that the event namespace when the getData is triggered corresponds to the name of the "value" property. But currently, as I mentioned in my previous post, the namespace will always (no matter what) be set to the first segment after the dot.

The consequence is:

var x = $({ name: "test" });
x.bind("getData.name", function() { console.log("name requested"); });
x.data("name"); // this statement does not run the event handler
x.data("some.name"); // but this one does

But of course it may be intentional behavior, it just is not clear to me why only the first namespace segment is always used in this case.

What I am trying to say is that if John Resig's presentation advertises some feature of jQuery then it can't be considered "experimental". No, it must be documented and it must work as expected. Otherwise the information on the web site must be corrected.

Another question is regarding attempt to trigger exclusive events. For example:

$this.triggerHandler( "setData" + parts[1] + "!", args );

I am sure you are aware of the fact that according to current implementation, only handlers with no namespaces at all will be subject to the "exclusive" behavior.

I mean triggerHandler("setData!", args) will trigger only those handlers which were subscribed to "setData" exclusively.

But triggerHandler("setData.sub!") will trigger not only "setData.sub" subscribers but also "setData.sub.sub", "setData.sub.sub.sub" and so on.

So it is not clear to me why the behavior is not consistent for no-namespace subscribers and the ones which subscribed to some particular namespace.

But sorry, I diverted and my main point is:

I can't agree that it is just a matter of undocumented experimental implementation. If release notes are wrong, then please correct it and notify jQuery users of the error. If John Resig's web site contains erroneous information within the presentation named "Things You Might Not Know About jQuery" then could you please communicate this information so that the error is also corrected. Otherwise it will result in "Wrong things I know about jQuery"

It would be great to have some feedback regarding the issues prior to jQuery 1.5 release

Thanks you once again for your answers!

scott.gon..

Re: jquery.fn.data - get/set/changeData events syntax

12 years ago

I'm really busy right now and don't have time to give a long explanation (I'll try to reply again later today when I have some time), but I wanted to give a very quick explanation of the intended behavior.

The getData and setData events were added as a way for plugins to manage options via .data(). For example, you could create a dialog plugin that listens for getData.dialog and setData.dialog and capture all .data() calls that have a namespace of dialog. So to set the title, you would call .data( "title.dialog", "new title" ) and then the plugin would handle that inside it's setData event handler (which has the dialog namespace).

You can see how we used to use this in jQuery UI by looking at some of the code from an old release. You'll notice that we did return values for the getData event (it used to work).

There have been a lot of changes to the events around .data() recently for performance and enhancements (additional events, use on objects, etc.) so it's likely that anything broken was an accident during those changes.

algorkov

Re: Re: jquery.fn.data - get/set/changeData events syntax

12 years ago

Thanks. I am looking forward to hear your explanations.

As a brief note, yes, I am aware of the fact that getter uses a value returned by getData event handler. It works as expected and it is not part of my questions.

algorkov

Re: jquery.fn.data - get/set/changeData events syntax

12 years ago

Any news?

Ok, I understand that jQuery Core team member all are very busy people unlike the rest of us, mere mortals

, so I'll narrow down my complaints to two simple items (you can read all the rest above):

1. result returned by setData event handler must be used to set actual element data object or plain object data.

2. it should be possible to prevent the data from being set, ideally using preventDefault() within setData event handler. In this case we can't use triggerHandler to trigger setData handlers. We would need to create event object explicitly and pass it to jQuery.event.trigger to be able to analyze isDefaultPrevented. Currently the preventDefault is executed within triggerHandler regardless of the event handler execution results.

"must" and "should" in the list above is not a product of my over opinionated mind. It is how the functionality should behave according to:

1. jQuery 1.4.3 release notes

2. Presentation on John Resig's web site

Thus, in my opinion the issues can't be covered by "experimental" or "not well documented" terms. If they are experimental and do not work as expected, you should probably update the release notes and do not mention the features elsewhere. Of course I may be wrong. Sorry in this case.

Thanks

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