SajidHussa says:

function editstudent(element) {

                 

               var table = document.getElementById("123");

               var index = element.closest('tr').rowIndex;          

               var id = table.rows[parseInt(index)].cells[1].innerHTML;

               alert(id);

               

 

           }

Use the below code.

function editstudent(element) {
    var row = element.parentNode.parentNode;
    var index = row.rowIndex;
    var id = row.cells[0].innerHTML;
    alert("Index : " + index + "\nId : " + id);
}