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。