select all checkboxes in a table javascript

function checkAll(bx,dg) {
                                        var tbl = document.getElementById(dg);

                                        for (var index = 1; index < tbl.rows.length; index++) {
                                            var cbs = tbl.rows[index].getElementsByTagName('input');
                                            for (var i = 0; i < cbs.length; i++) {
                                                if (cbs[i].type == 'checkbox') {
                                                    if (cbs[i].disabled == false) {
                                                        cbs[i].checked = bx.checked;
                                                        //alert(cbs[i].disabled);
                                                    }
                                                }
                                            }
                                        }
                                    }

ex: <input type="checkbox" id="chkAll" onclick="checkAll(this,'tableId" />