Simple Node.js Logger With Example

logger.util.js

/* eslint-disable no-console */

const _errorFormat = (error) => {
  return {
    name: error.name,
    message: error.message,
    stack: error.stack.split('\n').map((ele) => ele.trim()),
  };
};

const _prepareMetaData = (metaData) => {
  for (const i in metaData) {
    if (metaData[i] instanceof Error) {
      metaData[i] = _errorFormat(metaData[i]);
    }
  }

  return metaData;
};

const _write = (opts) => {
  const { logFunc, tag, level, message, metaData } = opts;
  const date = new Date();

  if (process.env.NODE_ENV !== 'test') {
    logFunc(
      JSON.stringify({
        tag: `${tag} <${level}>`,
        level,
        message,
        formattedDate: date.toISOString(),
        env: process.env.NODE_ENV,
        processId: process.pid,
        clusterType: process.env.CLUSTER_TYPE,
        timestamp: date.getTime(),
        metaData: _prepareMetaData(metaData),
      }),
    );

    logFunc(' ');
  }
};

const logger = (tag) => {
  return {
    log: (message, metaData = {}) => {
      _write({
        logFunc: console.log,
        level: 'log',
        tag,
        message,
        metaData,
      });
    },

    error: (message, metaData = {}) => {
      _write({
        logFunc: console.error,
        level: 'error',
        tag,
        message,
        metaData,
      });
    },
  };
};

module.exports = logger;

/*
  // server.js

  const express = require('express');
  const logger = require('./src/utils/logger.util.js')('server');

  const app = express();

  server.use((req, res, next) => {
    logger.log('request', {
      body: req.body,
      query: req.query,
      params: req.params,
      token: req.headers.authorization || null,
      path: req.path,
    });

    next();
  });

  app.listen(process.env.PORT, () => {
    logger.log(`Example app listening at http://localhost:${process.env.PORT}`);
  });

*/