Attempt to fix #1577.

lib/winston/create-logger.js

@@ -12,79 +12,93 @@ const config = require('./config');
 const Logger = require('./logger');
 const debug = require('diagnostics')('winston:create-logger');
 
+function isLevelEnabledFunctionName(level) {
+  return 'is' + level.charAt(0).toUpperCase() + level.slice(1) + 'Enabled';
+}
+
 /**
- * DerivedLogger to attach the logs level methods.
- * @type {DerivedLogger}
- * @extends {Logger}
+ * 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.
  */
-class DerivedLogger extends Logger {
+module.exports = function (opts = {}) {
+  //
+  // Default levels: npm
+  //
+  opts.levels = opts.levels || config.npm.levels;
+
   /**
-   * 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.
+   * DerivedLogger to attach the logs level methods.
+   * @type {DerivedLogger}
+   * @extends {Logger}
    */
-  constructor(options) {
-    super(options);
-    this._setupLevels();
+  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);
+    }
   }
 
-  /**
-   * Create the log level methods for the derived logger.
-   * @returns {undefined}
-   * @private
-   */
-  _setupLevels() {
-    Object.keys(this.levels).forEach(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;
-      }
+  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) <––> logger.info(msg) & logger.isInfoEnabled()
-      // this is not an arrow function so it'll always be called on the instance instead of a fixed place in the prototype chain.
-      this[level] = function (...args) {
-        // 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;
-          this._addDefaultMeta(info);
-          this.write(info);
-          return this;
-        }
+    //
+    // 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;
 
-        // When provided nothing assume the empty string
-        if (args.length === 0) {
-          this.log(level, '');
-          return this;
-        }
+      // 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);
+      }
 
-        // 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 this.log(level, ...args);
-      };
+      // When provided nothing assume the empty string
+      if (args.length === 0) {
+        self.log(level, '');
+        return self;
+      }
 
-      this[isLevelEnabledFunctionName(level)] = () => this.isLevelEnabled(level);
-    });
-  }
-}
+      // 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);
+    };
 
-function isLevelEnabledFunctionName(level) {
-  return 'is' + level.charAt(0).toUpperCase() + level.slice(1) + 'Enabled';
-}
+    DerivedLogger.prototype[isLevelEnabledFunctionName(level)] = function () {
+      return (this || logger).isLevelEnabled(level);
+    };
+  });
 
-/**
- * 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 = (opts = { levels: config.npm.levels }) => (
-  new DerivedLogger(opts)
-);
+  return logger;
+};