Node.js - Console

A console is a text-based user interface that allows you to interact with the computer's operating system or run code. With the console, you can write and execute commands or programs. It is also used for debugging and troubleshooting. The built-in library of Node.js includes the Console module. It provides functionality to print messages to IO streams, a functionality similar to the JavaScript console mechanism provided by web browsers.

The Console module’s functionality has two major parts −

Console class: The console class methods are console.log(), console.error() and console.warn() to display Node.js stream.

global console object: A predefined object that echoes logging, errors and warning messages to the standard output stream. It is used without calling require(‘console’).

The default usage of global console object is simple. The following code shows a typical usage of global console object to display logging, error and warning messages.

Example

// Welcome message
console.log('Welcome to Tutorialspoint!');

// Hello world message

console.log('hello world');

// printing to error stream

console.error(new Error('Oops... something went wrong'));

// print warning

const name = 'NodeJS Tutorial';

console.warn(`Warning ${name}! Warning!`);

Output

Welcome to Tutorialspoint!
hello world
Error: Oops... something went wrong
   at Object.<anonymous> (D:\nodejs\emailapp\main.js:11:15)
    at Module._compile (node:internal/modules/cjs/loader:1241:14)
	at Module._extensions..js (node:internal/modules/cjs/loader:1295:10)
    at Module.load (node:internal/modules/cjs/loader:1091:32)
    at Module._load (node:internal/modules/cjs/loader:938:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:83:12)
    at node:internal/main/run_main_module:23:47
Warning NodeJS Tutorial! Warning!

You can also customize the console object by designating the streams for reflecting the output and error logs. Declare an object of Console class and pass the stream objects as arguments.

The program below redirects the logs and errors to the two disk files.

const fs = require('fs');

const out = fs.createWriteStream('./stdout.log');

const err = fs.createWriteStream('./stderr.log');

const logger = new console.Console(out, err);

// Welcome message
logger.log('Welcome to Tutorialspoint!');

// Hello world message

logger.log('hello world');

// printing to error stream

logger.error(new Error('Oops... something went wrong'));

// print warning

const name = 'NodeJS Tutorial';

logger.warn(`Warning ${name}! Warning!`);

This will create two files stdout.log and stderr.log in the current directory, with the result of log(), error(), and warn() methods of console objects saved in them.

Console Methods

Following is a list of methods available with the console object.