Where is nodejs log file?

Question

There is no log file. Each node.js "app" is a separate entity. By default it will log errors to STDERR and output to STDOUT. You can change that when you run it from your shell to log to a file instead.

node my_app.js > my_app_log.log 2> my_app_err.log

Alternatively (recommended), you can add logging inside your application either manually or with one of the many log libraries:

• winston
• log4js
• ...

forever might be of interest to you. It will run your .js-File 24/7 with logging options. Here are two snippets from the help text:

[Long Running Process] The forever process will continue to run outputting log messages to the console. ex. forever -o out.log -e err.log my-script.js

and

[Daemon] The forever process will run as a daemon which will make the target process start in the background. This is extremely useful for remote starting simple node.js scripts without using nohup. It is recommended to run start with -o -l, & -e. ex. forever start -l forever.log -o out.log -e err.log my-daemon.js forever stop my-daemon.js

If you use docker in your dev you can do this in another shell: docker attach running_node_app_container_name

That will show you STDOUT and STDERR.

For nodejs log file you can use winston and morgan and in place of your console.log() statement user winston.log() or other winston methods to log. For working with winston and morgan you need to install them using npm. Example: npm i -S winston npm i -S morgan

Then create a folder in your project with name winston and then create a config.js in that folder and copy this code given below.

const appRoot = require('app-root-path');
const winston = require('winston');

// define the custom settings for each transport (file, console)
const options = {
  file: {
    level: 'info',
    filename: `${appRoot}/logs/app.log`,
    handleExceptions: true,
    json: true,
    maxsize: 5242880, // 5MB
    maxFiles: 5,
    colorize: false,
  },
  console: {
    level: 'debug',
    handleExceptions: true,
    json: false,
    colorize: true,
  },
};

// instantiate a new Winston Logger with the settings defined above
let logger;
if (process.env.logging === 'off') {
  logger = winston.createLogger({
    transports: [
      new winston.transports.File(options.file),
    ],
    exitOnError: false, // do not exit on handled exceptions
  });
} else {
  logger = winston.createLogger({
    transports: [
      new winston.transports.File(options.file),
      new winston.transports.Console(options.console),
    ],
    exitOnError: false, // do not exit on handled exceptions
  });
}

// create a stream object with a 'write' function that will be used by `morgan`
logger.stream = {
  write(message) {
    logger.info(message);
  },
};

module.exports = logger;

After copying the above code make make a folder with name logs parallel to winston or wherever you want and create a file app.log in that logs folder. Go back to config.js and set the path in the 5th line "filename: ${appRoot}/logs/app.log, " to the respective app.log created by you.

After this go to your index.js and include the following code in it.

const morgan = require('morgan');
const winston = require('./winston/config');
const express = require('express');
const app = express();
app.use(morgan('combined', { stream: winston.stream }));

winston.info('You have successfully started working with winston and morgan');