Find Control Inside GridView in Javascript

function SelectAll(id) {

            var grd = document.getElementById("<%= GridView1.ClientID %>");

            var cell;

            if (grd.rows.length > 0) {

                for (i = 1; i < grd.rows.length; i++) {

                    cell = grd.rows[i].cells[0];

                    for (j = 0; j < cell.childNodes.length; j++) {

                        if (cell.childNodes[j].type == "checkbox") {

                            cell.childNodes[j].checked = document.getElementById(id).checked;

                        }

                    }

                }

            }

        }