jQuery Grid Plugin - jqGrid

{name:'activity_scope',index:'activity_scope', width:250, editable:true, edittype:'custom',
                    editoptions:{
                        custom_element: function(value, options) {
                            return Parent.getActivityScopeElement(value, options);
                        },
                        custom_value: function(elem, operation, value) {
                            return Parent.getActivityScopeValue(elem, operation, value);
                        },
                        defaultValue: function() {
                            return 0;
                        }
                    },
                    formatter: function(cellvalue, options, rowObject) {
                        var scope = $j.parseJSON( Runtime.getParam('scope_activity')), ret = [], sum=0;
                        $j.extend(scope.buyer, scope.seller);
                        $j.each(scope.buyer, function(i, el) {
                            if(cellvalue & i) {
                                ret.push(el) ;
                            }
                        });
                        return ret.slice(', ') + '<input type="hidden" value="'+(cellvalue)+'" />';
                    },
                    unformat:function(cellvalue, options, rowObject) {
                        return $j(rowObject).find('input[type=hidden]').val();
                    },
                    stype: 'custom',
                    searchoptions: {
                        sopt:['cn'],
                        custom_element: function(value, options) {
                            return Parent.getActivityScopeElement(value, options);
                        },
                        custom_value: function (elem, operation, value) {
                            return Parent.getActivityScopeValue(elem, operation, value);
                        }
                    },
                    sorttype:'string',editrules:{custom:true, custom_func:Parent.checkActivityScope}, formoptions:{elmprefix: html.span("(*)", {'class':'prefix float_left'})} }

    this.getActivityScopeElement = function(value, options) {
        var scope = $j.parseJSON( Runtime.getParam('scope_activity') );
        var elemStr = '<table class="activity_scope"><thead><tr><th>Buyer's side</th><th>Seller's side</th></tr></thead><tbody>';
        elemStr += '<tr>';
        elemStr += '<td>';
        $j.each(scope.buyer, function(i, el) {
            var checked = i & value? 'checked="checked"' : '';
            elemStr += '<div><input type="checkbox" name="activity_scope" value="'+ i +'" '+checked+' /><label>'+ el +'</label></div>';
        });
        elemStr += '</td>';

        elemStr += '<td>';
        $j.each(scope.seller, function(i, el) {
            var checked = i & value? 'checked="checked"' : '';
            elemStr += '<div><input type="checkbox" name="activity_scope" value="'+ i +'" '+checked+' /><label>'+ el +'</label></div>';
        });
        elemStr += '</td>';

        elemStr += '</tr>';
        elemStr += '</tbody></table>';
        return $j(elemStr)[0];
    };

    this.getActivityScopeValue = function(elem, operation, value) {
        if(operation === 'get') {
            var val = 0;
            $j(elem).find("input:checked").each(function(i, el){
                val += parseInt( $j(el).val() );
            });
            return val;
        } else if(operation === 'set') {
            $j(elem).find("input").each(function(i, el){
                var checked = (parseInt( $j(el).val() ) & value) > 0;
                $j(el).attr('checked', checked);
            });
        }
    };