If you want to get the data id value from the html element like anchor tag, button or li when the user clicks, you can get using $(this).attr(“data-id”) and in newer versions >=1.4.3 we can use $(this).data().
<a data-id="321" class="upvote"></a>
$(".upvote").on("click", function () {
var id = $(this).attr("data-id"); // it will return string value 321
});
In newer versions >=1.4.3:
var id = $(this).data(); // it will return number 321