Log caller function name and line number

There does not seem to be a way to log the caller’s method name and line number. I know that this has already been requested with #200, but that issue was locked with the reason that such a function would be very slow. Given that a typical application would not excessively log thousands of log statements per second, it does not make a noticeably difference.

As you probably know, JavaScript provides the stack trace in the Error.stack property on construction of a new Error object. However, this is an unstructured string and needs to be parsed. V8 on the other hand has a feature allowing to retrieve the stack trace in its original structured form (before stringifying). This is described here: https://github.com/v8/v8/wiki/Stack-Trace-API

My current implementation on top of Winston looks like this. (It may not be a good implementation, I’m very new to JavaScript and Node/V8. 😃 )

// ES2015
const path = require('path');
const winston = require('winston');
function CustomError() {
  // Use V8's feature to get a structured stack trace
  const oldStackTrace = Error.prepareStackTrace;
  const oldLimit = Error.stackTraceLimit;
  try {
    Error.stackTraceLimit = 3; // <- we only need the top 3
    Error.prepareStackTrace = (err, structuredStackTrace) => structuredStackTrace;
    Error.captureStackTrace(this, CustomError);
    this.stack; // <- invoke the getter for 'stack'
  } finally {
    Error.stackTraceLimit = oldLimit;
    Error.prepareStackTrace = oldStackTrace;
  }
}
function getAndFormatStackTraceElement() {
  const stack = new CustomError().stack;
  const CALLER_INDEX = 2; // <- position in stacktrace to find deepest caller
  const element = stack[CALLER_INDEX];
  const fileName = path.basename(element.getFileName());
  return element.getFunctionName() + "(" + fileName + ":" + element.getLineNumber() + ")";
}
module.exports = {
  info(msg, ...vars) {
    winston.info(getAndFormatStackTraceElement() + ': ' + msg, ...vars);
  }
}

Credits go to @addaleax from: https://github.com/nodejs/node/issues/7749#issuecomment-232972234 The way the string is formatted and the module exports are defined, sure needs reworking, I guess.

This ticket could serve as a discussion on how a good PR would look like for Winston, adding this feature to the library.