Using data attributes with jQuery

I have this button:

<button type="button" class="themeChanger" data-themeValue="grid" value="Grid">
   <img src="templateImages/Icon_200.png" />                
</button>

And this jQuery:

$(".themeChanger").c开发者_C百科lick(function () { 
    alert($(this).attr("data-themeValue")); 
    alert($(this).data("themeValue")); 
});

For some reason the first alert shows "grid" like it should, but the second shows undefined. Is there something stupid I'm missing?

I think data will look on lowercases: alert($(this).data("themevalue")) //grid

or if you want to use themeValue you need to use:

edit:

I was wrong, it doesnt have anything to do with lowercases, you can use themeValue if you are having the attribute: data-theme-value then you call itwith $(element).data("themeValue")

<button class="themeChanger" data-themeValue="Theme1" data-theme-value="Theme2"></button>

$(".themeChanger").click(function() {
    var el = $(this);

    alert($(this).data("themeValue")); //Theme2
    alert($(this).data("themevalue")); //Theme1
});

As noted in this Learning jQuery article, HTML5 data-* attributes are handled by the browser->JS conversion in the same way that CSS names are handled--that is:

1. the leading data- is removed (a step not needed in the CSS name comparison I drew above)
   • data-specialInfo becomes specialInfo
   • data-more-specialInfo becomes more-specialInfo
2. the remaining attr name is split on -
   • specialInfo becomes [ specialInfo ]
   • more-specialInfo becomes [ more, specialInfo ]
3. the first of the resulting split parts is dropped to all lower case
   • [ specialInfo ] becomes [ specialinfo ]
   • [ more, specialInfo ] becomes [ more, specialInfo ] (no change as first part was already lower)
4. the rest of the resulting split parts are dropped to lower case, but their first letter is made upper case
   • [ specialinfo ] becomes [ specialinfo ] (no change because there were no other parts)
   • [ more, specialInfo ] becomes [ more, Specialinfo ]
5. The now case-modified parts are rejoined on empty string
   • [ specialinfo ] becomes specialinfo
   • [ more, Specialinfo ] becomes moreSpecialinfo

This being the case, your data-themeValue attribute is accessible via $(this).data("themevalue"). Whereas a data-theme-value attribute would be accessible via $(this).data("themeValue").

It's terribly confusing unless you recognize the mechanism in use.

The problem is the camel case. For clarity I'd stick to the data-theme-value format for your attributes.

http://jsfiddle.net/NkHEx/2/

jquery automatically converts .data('some-value') to data('someValue')

Note that both alert calls return grid

I think it is the camel casing of hyphenated words in the data tag implementation that is the gotcha here

Try this jsfiddle - http://jsfiddle.net/FloydPink/fb6Y6/

<button type="button" class="themeChanger" data-theme-value="grid" value="Grid">
   data-theme-value                
</button>

<button type="button" class="themeChanger" data-themeValue="grid" value="Grid">
   data-themeValue
</button>

$(".themeChanger").click(function () {
    alert($(this).attr("data-themeValue"));
    alert($(this).data("themeValue"));
});