winstonjs/winston · error · Error

Logger is required for profiling

Error message

Logger is required for profiling

What it means

Profiler objects time operations and log a duration through their associated Logger. The constructor strictly validates the argument: it must be a real Logger instance (not a plain object or array), otherwise timing results could never be logged, so it throws.

Source

Thrown at lib/winston/profiler.js:25

'use strict';
/**
 * TODO: add class description.
 * @type {Profiler}
 * @private
 */
class Profiler {
  /**
   * Constructor function for the Profiler instance used by
   * `Logger.prototype.startTimer`. When done is called the timer will finish
   * and log the duration.
   * @param {!Logger} logger - TODO: add param description.
   * @private
   */
  constructor(logger) {
    const Logger = require('./logger');
    if (typeof logger !== 'object' || Array.isArray(logger) || !(logger instanceof Logger)) {
      throw new Error('Logger is required for profiling');
    } else {
      this.logger = logger;
      this.start = Date.now();
    }
  }

  /**
   * Ends the current timer (i.e. Profiler) instance and logs the `msg` along
   * with the duration since creation.
   * @returns {mixed} - TODO: add return description.
   * @private
   */
  done(...args) {
    if (typeof args[args.length - 1] === 'function') {
      // eslint-disable-next-line no-console
      console.warn('Callback function no longer supported as of winston@3.0.0');
      args.pop();
    }

View on GitHub (pinned to ff0b79de85)

Solutions

1. Use `logger.startTimer()` / `profile()` on a real winston Logger instead of constructing Profiler manually.
2. Ensure exactly one winston version is installed (`npm ls winston`) so `instanceof` checks pass.
3. Pass the actual Logger instance returned by `winston.createLogger()`, not a stub or plain object.
4. In tests, use the real Logger or a class that extends it rather than a duck-typed mock.

Example fix

// before
const profiler = new winston.Profiler({ log: () => {} }); // plain object

// after
const logger = winston.createLogger({ transports: [new winston.transports.Console()] });
const timer = logger.startTimer();
timer.done({ message: 'work finished' });

const Logger = require('winston/lib/winston/logger');
if (!(maybeLogger instanceof Logger)) {
  throw new TypeError('Profiler requires an actual winston Logger instance');
}

function isRealLogger(x) { return x instanceof require('winston').Logger; }

try {
  const p = new winston.Profiler(logger);
} catch (err) {
  if (err.message === 'Logger is required for profiling') {
    const p = logger.startTimer();
  } else { throw err; }
}

When it happens

Trigger: Calling `new winston.Profiler(...)` (or `logger.startTimer()` internals) with `undefined`, a plain object, an array, or a non-Logger object; also passing something that looks like a logger but was created by another library or an older winston copy (fails the `instanceof Logger` check).

Common situations: Duplicated winston in node_modules (two copies -> instanceof mismatch); mocking a logger in tests with a plain object stub then calling startTimer; calling Profiler directly instead of via `logger.startTimer()`.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Logger is required to handle exceptions
• Logger is required to handle rejections
• ExceptionStream requires a TransportStream instance.
• Transports must WritableStreams in objectMode. Set { objectM
• RejectionStream requires a TransportStream instance.

AI-assisted analysis of winstonjs/winston@ff0b79de85 (2026-08-31). Data as JSON: /api/errors/71a5e4d2f5351b6e. Report an issue: GitHub.