winston/lib/winston/create-logger.js

A logger for just about everything.

/**
 * create-logger.js: Logger factory for winston logger instances.
 *
 * (C) 2010 Charlie Robbins
 * MIT LICENCE
 */

'use strict';

const { LEVEL } = require('triple-beam');
const config = require('./config');
const Logger = require('./logger');
const debug = require('@dabh/diagnostics')('winston:create-logger');

function isLevelEnabledFunctionName(level) {
  return 'is' + level.charAt(0).toUpperCase() + level.slice(1) + 'Enabled';
}

/**
 * Create a new instance of a winston Logger. Creates a new
 * prototype for each instance.
 * @param {!Object} opts - Options for the created logger.
 * @returns {Logger} - A newly created logger instance.
 */
module.exports = function (opts = {}) {
  //
  // Default levels: npm
  //
  opts.levels = opts.levels || config.npm.levels;

  /**
   * DerivedLogger to attach the logs level methods.
   * @type {DerivedLogger}
   * @extends {Logger}
   */
  class DerivedLogger extends Logger {
    /**
     * Create a new class derived logger for which the levels can be attached to
     * the prototype of. This is a V8 optimization that is well know to increase
     * performance of prototype functions.
     * @param {!Object} options - Options for the created logger.
     */
    constructor(options) {
      super(options);
    }
  }

  const logger = new DerivedLogger(opts);

  //
  // Create the log level methods for the derived logger.
  //
  Object.keys(opts.levels).forEach(function (level) {
    debug('Define prototype method for "%s"', level);
    if (level === 'log') {
      // eslint-disable-next-line no-console
      console.warn('Level "log" not defined: conflicts with the method "log". Use a different level name.');
      return;
    }

    //
    // Define prototype methods for each log level e.g.:
    // logger.log('info', msg) implies these methods are defined:
    // - logger.info(msg)
    // - logger.isInfoEnabled()
    //
    // Remark: to support logger.child this **MUST** be a function
    // so it'll always be called on the instance instead of a fixed
    // place in the prototype chain.
    //
    DerivedLogger.prototype[level] = function (...args) {
      // Prefer any instance scope, but default to "root" logger
      const self = this || logger;

      // Optimize the hot-path which is the single object.
      if (args.length === 1) {
        const [msg] = args;
        const info = msg && msg.message && msg || { message: msg };
        info.level = info[LEVEL] = level;
        self._addDefaultMeta(info);
        self.write(info);
        return (this || logger);
      }

      // When provided nothing assume the empty string
      if (args.length === 0) {
        self.log(level, '');
        return self;
      }

      // Otherwise build argument list which could potentially conform to
      // either:
      // . v3 API: log(obj)
      // 2. v1/v2 API: log(level, msg, ... [string interpolate], [{metadata}], [callback])
      return self.log(level, ...args);
    };

    DerivedLogger.prototype[isLevelEnabledFunctionName(level)] = function () {
      return (this || logger).isLevelEnabled(level);
    };
  });

  return logger;
};