Expressjs Server Monitoring with Winston + Morgan

logger.js

const { createLogger, format, transports } = require("winston");

// https://github.com/winstonjs/winston#logging
// { error: 0, warn: 1, info: 2, verbose: 3, debug: 4, silly: 5 }
const level = process.env.LOG_LEVEL || "debug";

function formatParams(info) {
  const { timestamp, level, message, ...args } = info;
  const ts = timestamp.slice(0, 19).replace("T", " ");

  return `${ts} ${level}: ${message} ${Object.keys(args).length
    ? JSON.stringify(args, "", "")
    : ""}`;
}

// https://github.com/winstonjs/winston/issues/1135
const developmentFormat = format.combine(
  format.colorize(),
  format.timestamp(),
  format.align(),
  format.printf(formatParams)
);

const productionFormat = format.combine(
  format.timestamp(),
  format.align(),
  format.printf(formatParams)
);

let logger;

if (process.env.NODE_ENV !== "production") {
  logger = createLogger({
    level: level,
    format: developmentFormat,
    transports: [new transports.Console()]
  });

} else {
  logger = createLogger({
    level: level,
    format: productionFormat,
    transports: [
      new transports.File({ filename: "error.log", level: "error" }),
      new transports.File({ filename: "combined.log" })
    ]
  });
}

module.exports = logger;

package.json

{
  "name": "expressjslogging",
  "license": "MIT",
  "dependencies": {
    "express": "^4.16.2",
    "morgan": "^1.9.0",
    "winston": "^3.0.0-rc1"
  }
}

server.js

const express = require("express");
const logger = require("./logger");
const morgan = require("morgan");

const PORT = 3000;
const app = express();

const morganFormat = process.env.NODE_ENV !== "production" ? "dev" : "combined";

app.use(
  morgan(morganFormat, {
    skip: function(req, res) {
      return res.statusCode < 400;
    },
    stream: process.stderr
  })
);

app.use(
  morgan(morganFormat, {
    skip: function(req, res) {
      return res.statusCode >= 400;
    },
    stream: process.stdout
  })
);

app.get("/", function(req, res) {
  logger.debug("Debug statement");
  logger.info("Info statement");
  res.send(req.method + ' ' + req.originalURL);
});

app.get("/error", function(req, res) {
  throw new Error('Problem Here!');
});

// All errors are sent back as JSON
app.use((err, req, res, next) => {
  // Fallback to default node handler
  if (res.headersSent) {
    next(err);
    return;
  }

  logger.error(err.message, {url: req.originalUrl});

  res.status(500);
  res.json({ error: err.message });
});

// Start server
app.listen(PORT, function() {
  logger.info("Example app listening on port " + PORT);
  logger.debug("More detailed log", {PORT});
});