what is data id tag in javascript code example

Example 1: jquery get data attribute value

/* html */
<a data-id="123">link</a>

/* js */
$(this).attr("data-id") // returns string "123"

$(this).data("id") // returns number 123 (jQuery >= 1.4.3 only)

Example 2: data id tag

var dataId = $(this).attr("data-id");