nodejs for loop to get database document

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I'm new to nodejs and is trying to understand its asynchronous idea. In the following code snippet, I'm trying to get two documents from mongodb database randomly. It works fine, but looks very ugly because of the nested callback functions. If I want to get 100 documents instead of 2, that would be a disaster.

app.get('/api/two', function(req, res){
        dataset.count(function(err, count){
                var docs = [];
                var rand = Math.floor(Math.random() * count);
                dataset.findOne({'index':rand}, function(err, doc){
                        docs.push(doc);
                        rand = Math.floor(Math.random() * count);
                        dataset.findOne({'index':rand}, function(err, doc1){
                                docs.push(doc1);
                                res.json(docs);
                        });
                });
        });
});

So I tried to use for-loop instead, however, the following code just doesn't work, and I guess I misunderstand the asynchronous method idea.

app.get('/api/two', function(req, res){
        dataset.count(function(err, count){
                var docs = []
                for(i = 0; i < 2 ; i++){
                        var rand = Math.floor(Math.random() * count);
                        dataset.findOne({'index':rand}, function(err, doc){
                                docs.push(doc);
                        });
                }
                res.json(docs);
        });
});

Can anyone help me with that and explain to me why it doesn't work? Thank you very much.

asked 29 secs ago

Idealist

62