winston-asynchandler/src/logger.js

Production-grade async error handler for Express with Winston logger and standard API responses.

import { createLogger, format, transports } from "winston";
import fs from "fs";
import path from "path";

const { combine, timestamp, printf, colorize } = format;

const logDir = path.resolve("logs");
if (!fs.existsSync(logDir)) {
  fs.mkdirSync(logDir);
}

const logFormat = printf(({ level, message, timestamp }) => {
  return `[${timestamp}] ${level}: ${message}`;
});

export const logger = createLogger({
  level: "info",
  format: combine(timestamp({ format: "YYYY-MM-DD HH:mm:ss" }), logFormat),
  transports: [
    new transports.File({
      filename: path.join(logDir, "error.log"),
      level: "error",
    }),
    new transports.File({ filename: path.join(logDir, "combined.log") }),
  ],
});

if (process.env.NODE_ENV !== "production") {
  logger.add(
    new transports.Console({
      format: combine(
        colorize(),
        timestamp({ format: "YYYY-MM-DD HH:mm:ss" }),
        logFormat
      ),
    })
  );
}