dump jquery object in an alert box

Why don’t you just accumulate the values in an array, then display the whole array (for instance, using JSON)? Example:

var acc = []
$.each(a, function(index, value) {
    acc.push(index + ': ' + value);
});
alert(JSON.stringify(acc));

In any case, I’d suggest using a debug tool like Firebug. So you could just use console.log(a) and be able to navigate freely through the objects’s fields.