Don't use the jQuery .data() method. Use .attr() instead. (lookfirst.com)

As far as I can tell this might just be false. If you go to github.com (a random site which happens to include query 1.7.1 -- the latest version), open the console in either firebug or webkit inspector, and run the author's example:

    var foo = $("body");
    foo.data("mykey", "1.410");
    foo.data("mykey");

...you get your original "1.410", not 1.41 as the author reports.

Secondly, he says there are "several bug reports on the jQuery website, where people are also confused by this behavior and all of them get closed with a wontfix" but links to none of them. Linking to them should be trivial and they'd help his case (or at least make it easy for me to figure out why he sees a bug and I don't). I searched and couldn't find any.

Finally, you shouldn't use .attr() to store arbitrary data as he recommends. Hanging javascript data off of DOM nodes will cause serious memory leaks if you're not careful. That's the reason .data() exists in the first place. See the "Cicular References" section of Understanding and Solving Internet Explorer Leak Patterns: http://msdn.microsoft.com/en-us/library/Bb250448

  elem.data('foo', { 'a':1, 'b':2 });
  elem.data('foo'); // Returns the object

  elem.attr('foo', { 'a':1, 'b':2 });
  elem.attr('foo'); // Returns "[object Object]"

   <div id="test" data-foo="1.1"> 
   $('#test').data('bar', '1.1');
   typeof $('#test').data('foo'); // number
   typeof $('#test').data('bar'); // string

   <div data-emoticon="0.0" />

  Every attempt is made to convert the string to a 
  JavaScript value (this includes booleans, numbers, 
  objects, arrays, and null) otherwise it is left as a 
  string. To retrieve the value's attribute as a string 
  without any attempt to convert it, use the attr() method.

I wasn't aware of this. This looks like a bad design choice indeed. I hate when libraries convert stuff implicitly for you. html5's localStorage has a similar problem. Only, it converts whatever you are trying to store into a string. Would be better if it accepted only strings and threw an error if you tried to store something else, imho.

This is bad advice. data() takes care of many details that .attr() does not, such as preventing IE memory leaks or trampling an existing DOM property.

I don't understand the issue. He is putting in 1.410 and gets 1.41? Isn't that the expected result?

In what way does the author think this behaviour is wrong? 1.410 === 1.41

If he wanted to store a string, then he should actually store a string. .data() is just a thin wrapper around getting and setting values on an object, which initialises its initial values from the data-* attributes on the element in question (which should always be strings).

Here is another example of what I'm talking about:

http://jsfiddle.net/KwjvA/

So, first the article talks about strings, but then does all of it's examples using floats. We all make mistakes. Hopefully we can help with that.

The root issue here is that the developer assumed how somethig worked, and didnt bother to learn how it actually worked.

I actually do have issues with data attribute for this exact reason, but that is no excuse for not looking up how it actually works.

The jquery docs say that it stores as Json. 1.4000 in Json is a float. Use data-key="'1.400'" to get a string.

I hade my gripes with .data too:

    <div id="test" data-foo="bar"></div>
    <script>
    $("#test").removeData('foo');
    console.log("#test").data('foo'));
    //bar
    </script>

The thing is removeData is pretty much useless because it only removes data from the jQuery cache, but if the data is missing from the cache jQuery will look in the DOM anyway.