[NodeJS] Get the current function name or any other function while using strict mode

functionName.js

'use strict';

const findFirstOccurrence = (string, searchElements, fromIndex = 0) => {
  let min = string.length;
  for (let i = 0; i < searchElements.length; i += 1) {
    const occ = string.indexOf(searchElements[i], fromIndex);
    if (occ !== -1 && occ < min) {
      min = occ;
    }
  }
  return (min === string.length) ? -1 : min;
}

const functionName = (func = null) => {
  if (func) {
    if (func.name) {
      return func.name;
    }
    const result = /^function\s+([\w\$]+)\s*\(/.exec(func.toString());
    return result ? result[1] : '';
  }
  const obj = {};
  Error.captureStackTrace(obj, functionName);
  const {stack} = obj;
  const firstCharacter = stack.indexOf('at ') + 3;
  const lastCharacter = findFirstOccurrence(stack, [' ', ':', '\n'], firstCharacter);
  return stack.slice(firstCharacter, lastCharacter);
}

module.exports = functionName;

stacktracey seems to work cross browser pretty well

Great job. This is exactly what I was looking for without instantiating a new Error (although it still parses a call stack). Confirmed working in Node v16.13.0. It also may not be clear until you're using it that just calling the function without passing a function will get the current function's name.