Node.js Basics — Debugging Apps

Node.js is a popular runtime platform to create programs that run on it.

It lets us run JavaScript outside the browser.

In this article, we’ll look at how to start using Node.js to create programs.

Logging with Morgan

To let us debug our Node.js apps easily, we can use the morgan package to add a logger into our app.

To install it, we run:

npm i morgan

Then we can use it by writing:

const Morgan = require('morgan'),
  Router = require('router'),
  http = require('http');
router = new Router();
router.use(Morgan('tiny'));

http.createServer(function(request, response) {
  router(request, response, function(error) {
    if (!error) {
      response.writeHead(404);
    } else {
      console.log(error.message, error.stack);
      response.writeHead(400);
    }
    response.end('n');
  });
}).listen(8000);

We add the Morgan middleware into our router by calling the router.use method with the Morgan('tiny') middleware.

Now we see logging in our app.

Now we can remove the console.log and write:

const Morgan = require('morgan'),
  Router = require('router'),
  http = require('http');
router = new Router();
router.use(Morgan('tiny'));

http.createServer(function(request, response) {
  router(request, response, function(error) {
    let info = process.versions;
    info = JSON.stringify(info);
    response.writeHead(200, {
      'Content-Type': 'application/json'
    });
    response.end(info);

  });
}).listen(8000);

and still get logging.

Alternatively, we can use the bunyan package to do the logging.

To install it, we run:

npm i bunyan

Then we can use it by writing:

const Bunyan = require('bunyan');
const logger = Bunyan.createLogger({
  name: 'example'
});
logger.info('Hello logging');

We require the bunyan package. Then we create our logger with the createLogger method.

The name is the name of the logger.

Then we use the logger.info method to log anything we want.

We can log items with other levels of logging by using various methods.

For example, we can write:

const Bunyan = require('bunyan');
const logger = Bunyan.createLogger({
  name: 'example'
});
logger.info('Hello logging');
logger.trace('Trace');
logger.debug('Debug');
logger.info('Info');
logger.warn('Warn');
logger.error('Error');
logger.fatal('Fatal');

Then we get object with various values of the level property logged to let us know the severity level of the log item.

We can also write:

const Bunyan = require('bunyan');
const logger = Bunyan.createLogger({
  name: 'example',
  level: Bunyan.TRACE

});
logger.info('Hello logging');
logger.trace('Trace');
logger.debug('Debug');
logger.info('Info');
logger.warn('Warn');
logger.error('Error');
logger.fatal('Fatal');

to set the level in when we call createLogger .

With Bunyan, we can also write the logged data to a file.

To do that, we write:

const Bunyan = require('bunyan');
const logger = Bunyan.createLogger({
  name: 'example',
  streams: [{
      level: Bunyan.INFO,
      path: './log.log'
    },
    {
      level: Bunyan.INFO,
      stream: process.stdout
    }
  ]
});
logger.info('Hello logging');
logger.trace('Trace');
logger.debug('Debug');
logger.info('Info');
logger.warn('Warn');
logger.error('Error');
logger.fatal('Fatal');

We add the streams property to add objects to specify where the log data goes.

The first entry of the streams array has the path property to specify the location to write to.

The 2nd object specifies that we write to stdout, which means we print the items on the screen.

Conclusion

We can add logging with various loggers.

We can use Morgan or Bunyan to add logging capabilities to our Node.js apps.