MongoDB Node findone how to handle no results?

Im using the npm mongodb driver with node.

I have

collection.findOne({query}, function(err, result) {
    //do something
}

The problem is say I dont have any results, err is still null whether I find a result or don't. How would I know that there were no results found with the query?

I've also tried

info = collection.findOne(....

But the info is just undefined (it looked asynchronous so I didn't think it was the way to go anyway..)

Not finding any records isn't an error condition, so what you want to look for is the lack of a value in result. Since any matching documents will always be "truthy", you can simply use a simple if (result) check. E.g.,

collection.findOne({query}, function(err, result) {
    if (err) { /* handle err */ }

    if (result) {
        // we have a result
    } else {
        // we don't
    }
}

All of these answers below are outdated. findOne is deprecated. Lastest 2.1 documentation proposes to use

find(query).limit(1).next(function(err, doc){
   // handle data
})