mongo join在node.js中不起作用

我正在使用mongo join连接node.js中的两个集合。下面的代码显示了该查询，但它没有连接两个集合。谁来帮帮我

某物

var client=newdb（config.dbname，新服务器（config.host，config.port1））；
client.open（函数（err，client）{
client.collection（'proInfo'，函数（err，proInfo）{
proInfo.find（{}，函数（err，游标）{
var join=new join（客户端）.on({
字段：“\u id”//
var client = new Db(config.dbname, new Server(config.host, config.port1));
            client.open(function(err, client) {
                client.collection('proInfo', function(err, proInfo) {
                    proInfo.find({}, function(err, cursor) {
                        var join = new Join(client).on({
                            field: '_id', // <- field in proInfo doc 
                            to: 'purchasedItemId',// <- field in purchased doc. treated as ObjectID automatically. 
                            from: 'purchased'  // <- collection name for purchased doc 
                        });   
                        join.toArray(cursor, function(err, joinedDocs) {
                        // handle array of joined documents here 
                        console.log(joinedDocs);
                        });


                    });
                });  
            });