Check out example codes for "js increment safety value html". It will help you in understanding the concepts better.

Code Example 1

function addRow(tableID) {

        var table = document.getElementById(tableID);

        var rowCount = document.getElementById(tableID).getElementsByTagName('tbody')
        [1].getElementsByTagName('tr').length;
        var row = table.insertRow(rowCount +1);

        var cell1 = row.insertCell(0);
        var element1 = document.createElement("input");
        element1.type = "hidden";
        element1.name = "Q[]";
        element1.value = rowCount +1;
        cell2.appendChild(element1);
        cell2.innerHTML = rowCount +1;
}

function deleteRow(tableID) {
        try {
        var table = document.getElementById(tableID);
        var rowCount = table.rows.length;

        for(var i=0; i<rowCount; i++) {
            var row = table.rows[i];
            var chkbox = row.cells[0].childNodes[0];
            if(null != chkbox && true == chkbox.checked) {
                table.deleteRow(i);
                rowCount--;
                i--;
            }


        }
        }catch(e) {
            alert(e);
        }
}

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