express-sequelize-backend-template/utils/logger.js

const path = require("path");

const { createLogger, transports, config, format } = require('winston');
const { combine, label, timestamp, printf, errors } = format;

const typedefs = require("../typedefs");

const getLabel = (callingModule) => {
	if (!callingModule.filename) return "repl";
	const parts = callingModule.filename?.split(path.sep);
	return path.join(parts[parts.length - 2], parts.pop());
};

const allowedErrorKeys = ["name", "code", "message", "stack"];

const metaFormat = (meta) => {
	if (Object.keys(meta).length > 0)
		return '\n' + JSON.stringify(meta, null, "\t");
	return '';
}

const logFormat = printf(({ level, message, label, timestamp, ...meta }) => {
	if (meta.error) { // if the error was passed
		for (const key in meta.error) {
			if (!allowedErrorKeys.includes(key)) {
				delete meta.error[key];
			}
		}
		const { stack, ...rest } = meta.error;
		return `${timestamp} [${label}] ${level}: ${message}${metaFormat(rest)}\n` +
			`${stack ?? ''}`;
	}
	return `${timestamp} [${label}] ${level}: ${message}${metaFormat(meta)}`;
});

/**
 * Creates a curried function, and call it with the module in use to get logs with filename
 * @param {typedefs.Module} callingModule The module from which the logger is called
 */
const curriedLogger = (callingModule) => {
	let winstonLogger = createLogger({
		levels: config.npm.levels,
		format: combine(
			errors({ stack: true }),
			label({ label: getLabel(callingModule) }),
			timestamp({ format: 'YYYY-MM-DD HH:mm:ss' }),
			logFormat,
		),
		transports: [
			new transports.Console({ level: 'info' }),
			new transports.File({
				filename: __dirname + '/../logs/debug.log',
				level: 'debug',
				maxsize: 10485760,
			}),
			new transports.File({
				filename: __dirname + '/../logs/error.log',
				level: 'error',
				maxsize: 1048576,
			}),
		]
	});
	winstonLogger.on('error', (error) => winstonLogger.error("Error inside logger", { error }));
	return winstonLogger;
}

module.exports = curriedLogger;