jQuery Forum

JΛ̊KE

It's converted to lower case because the specification says so:

jQuery has .data() and $.data(), but they're not really the same thing. It uses the data attributes to initialize an internal object, but when you update with .data() it only changes the internal object.

I wondered about performance. According to this jsPerf, .data() is 90% slower! (I tried it on desktop Chrome - it will be different in every browser.) 

But it is a poor jsPerf, as it doesn't distinguish between read and write. It does an equal number of reads and writes, and does not report separate results. Maybe there is a better jsPerf.

Surprisingly, jQuery $.data() doesn't suffer the huge performance hit of .data().

jQuery will convert JSON in data- to objects. I use jQuery .data() this way, rather than having multiple data- attributes. Then I just reference my object.

But it is (or perhaps was perceived as...) enough of a performance issue that jQuery Mobile 1.5 (currently in alpha test) removes a lot of data- attributes from previous versions, favoring CSS classes instead, citing performance.

It's not something that developers of typical websites or apps are likely to face in their own work. It *might* be an issue for a widget library like JQM, which manipulates the DOM to "enhance" elements, and may need to enhance hundreds or thousands of elements. (One might argue that a webpage with hundreds or thousands of widgets is a bad idea - and I would agree!)

I think, though, that the browsers have improved faster than the JQM team is able to produce new versions, so the change is probably moot.

I use dataset whenever I have code that does not/can not support ancient browsers. Even though it may not be as efficient as setAttribute. It’s the correct code to use, and it will only get faster.

I have been using the slim versions of jQuery lately. I use fewer and fewer of the "old" jQuery features that have since been implemented by browser.

JΛ̊KE

The author muddied the waters a bit by also including read/write DOM properties. But data- attributes don't create properties!

It does highlight, though, that if you need to save some data and associate it with a node, the fastest way is to add your own custom property. Setting and accessing properties is MUCH faster than attributes!

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I remember when it might take jQuery Mobile several seconds to enhance a page, particularly if it had a listview! I don't know if JQM has gotten that much better, or the browsers and hardware have gotten that much better. Probably both, as JQM simplified the enhanced markup.

I dealt with it by just not using Listviews. It's easy enough to make your own CSS for a list, and there really wasn't anything else I wanted from the Listview other than a nice appearance.