MongoDB - How can I get the size of a collection using Node.js?

.count() is an asynchronous function, just like .find() is.

Try the following code:

collection.count({}, function(error, numOfDocs) {
    console.log('I have '+numOfDocs+' documents in my collection');
    // ..
});

The first argument to .count() should be a search query. Since you want to count all documents, I'm passing an empty object {} as a search query.