How to get from an element all the data set using the data method?

This has been asked before. My answer from there, since it is a good question:

jQuery stores all the data information in the jQuery.cache internal variable. It is possible to get all the data associated with a particular object with this simple but helpful plugin:

jQuery.fn.allData = function() {
    var intID = jQuery.data(this.get(0));
    return(jQuery.cache[intID]);
};

With this in place, you can do this:

$('#myelement').data('test1','yay1')
               .data('test2','yay2')
               .data('test3','yay3');

$.each($('#myelement').allData(), function(key, value) {
    alert(key + "=" + value);
});

Alternatively, you can simply store an object:

$('#myelement').data('data', {test1:'yay1',test2:'yay2',test3:'yay3'});