Logging

You can change the log level, filter on classes to allow only specific classes to log, and provide your own logger implementation.

Setting Log level

The driver allows logging at three different levels: debug, info and error. The default level is error. The following example demonstrates how to set the logger to debug.

const MongoClient = require('mongodb').MongoClient;
const Logger = require('mongodb').Logger;
const assert = require('assert');

// Connection URL
const url = 'mongodb://localhost:27017';
// Database Name
const dbName = 'myprojeect';

const client = new MongoClient(url);
// Use connect method to connect to the server
client.connect(function(err) {
  assert.equal(null, err);
  console.log("Connected correctly to server");

  // Set debug level
  Logger.setLevel('debug');

  const db = client.db(dbName);

  // Execute command {ismaster:true} against db
  db.command({ismaster:true}, function(err, d) {
    assert.equal(null, err);
    client.close();
  });
});

Filtering On specific classes

You can set the Logger to only log specific class names. The following example demonstrates how to log only the Db class.

const MongoClient = require('mongodb').MongoClient;
const Logger = require('mongodb').Logger;
const assert = require('assert');

// Connection URL
const url = 'mongodb://localhost:27017';
// Database Name
const dbName = 'myprojeect';

const client = new MongoClient(url);
// Use connect method to connect to the server
client.connect(function(err) {
  assert.equal(null, err);
  console.log("Connected correctly to server");

  // Set debug level
  Logger.setLevel('debug');
  // Only log statements on 'Db' class
  Logger.filter('class', ['Db']);

  const db = client.db(dbName);

  // Execute command {ismaster:true} against db
  db.command({ismaster:true}, function(err, d) {
    assert.equal(null, err);
    client.close();
  });
});

Driver classes available for filtering:

• Db: The Db instance log statements
• Server: A server instance (either standalone, a mongos or replica set member)
• ReplSet: Replica set related log statements
• Mongos: Mongos related log statements
• Cursor: Cursor log statements
• Pool: Connection Pool specific log statements
• Connection: Singular connection specific log statements
• Ping: Replica set ping inquiry log statements

You can add your own classes to the logger by creating your own logger instances.

const Logger = require('mongodb').Logger;
const assert = require('assert');

class A {
  constructor() {
    this.logger = new Logger('A');
  }

  do() {
    if (this.logger.isInfo()) {
      this.logger.info('logging A', {});
    }
  }
}

// Execute A
const a = new A();
a.do();

Custom logger

The following example demonstrates how to define a custom logger.

const MongoClient = require('mongodb').MongoClient;
const Logger = require('mongodb').Logger;
const assert = require('assert');

// Connection URL
const url = 'mongodb://localhost:27017';
// Database Name
const dbName = 'myprojeect';

const client = new MongoClient(url);
// Use connect method to connect to the server
client.connect(function(err) {
  assert.equal(null, err);
  console.log("Connected correctly to server");

  // Set debug level
  Logger.setLevel('debug');
  
  // Set our own logger
  Logger.setCurrentLogger(function(msg, context) {
    console.log(msg, context);
  });

  const db = client.db(dbName);

  // Execute command {ismaster:true} against db
  db.command({ismaster:true}, function(err, d) {
    assert.equal(null, err);
    client.close();
  });
});