Cookbooks
JavaScript
Chapter 5. Good Coding Practices
Logging

JavaScript:
Logging

How to:

Out of the box, JavaScript offers a simple way to log messages to the console:

console.log('This will be logged to the console');

// Output:
// This will be logged to the console

But real-world apps require more than just printing messages to the console. Libraries like Winston or Pino can be introduced to manage logs effectively:

// Using Winston for advanced logging
const winston = require('winston');

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.json(),
  transports: [
    new winston.transports.File({ filename: 'combined.log' })
  ],
});

logger.info('Hello, this is a logging event with Winston');
// This log is written to 'combined.log' in JSON format

Sample combined.log output:

{"message":"Hello, this is a logging event with Winston","level":"info"}

Deep Dive

Logging has been essential since the early days of computing; system operators would peruse logs to understand system performance and diagnose problems. Fast forward to modern development, and we’ve shifted from simple log files to structured and searchable log management systems.

Alternatives to console or file-based logging in JavaScript include utilizing cloud-based logging services such as Loggly, Datadog, or ELK Stack (Elasticsearch, Logstash, Kibana) which can aggregate logs from multiple sources, offer visualization tools and advanced analytics.

When implementing logging, consider the following:

  • Level of Detail: Including debug, info, warning, error, and critical.
  • Performance: Excessive logging can impact application performance.
  • Security: Be cautious of logging sensitive information.
  • Format: Structured logs (like JSON) make it easier to search and parse logs.
  • Retention Policies: Old logs need to be archived or purged to save space.

A practical logging strategy defines what to log, where to log it, and how long to keep it around for, balancing informative insight against performance and privacy considerations.

See Also

Check out these resources for a deeper dive:

Handling errorsOrganizing code into functions