在MongoDB中，获取集合中的记录数可以使用countDocuments()方法。该方法返回一个promise，可以使用then()方法来获取结果。
以下是一个示例：
const MongoClient = require('mongodb').MongoClient;const uri = "mongodb+srv://<username>:<password>@<cluster-url>/<database>?retryWrites=true&w=majority";MongoClient.connect(uri, function(err, client) { if(err) { console.log('Error occurred while connecting to MongoDB Atlas...\n',err); } console.log('Connected to MongoDB Atlas...'); const collection = client.db("<database>").collection("<collection>"); collection.countDocuments() .then(count => { console.log("Number of documents in the collection: ", count); }) .catch(err => { console.log("Error occurred while counting documents:\n", err); }) .finally(() => { client.close(); });});请注意，<username>、<password>、<cluster-url>、<database>和<collection>都需要替换为适当的值。
