Inheriting from the Error object - where is the message property?

Question

I noticed a strange behavior while defining custom error objects in Javascript:

function MyError(msg) {
    Error.call(this, msg);
    this.name = \"MyError\         


        

Answer 1

I like a lot to make reusable .js files that I put in almost any project I participate. When i have time it will become a module.

For my errors i create a exceptions.js file and add it on my files.

Here is the example of the code inside this file:

const util = require('util');

/**
 * This exception should be used when some phat of code is not implemented.
 * @param {String} message Error message that will be used inside error.
 * @inheritDoc Error
 */
function NotImplementedException(message) {
  this.message = message;
  Error.captureStackTrace(this, NotImplementedException);
}

util.inherits(NotImplementedException, Error);

NotImplementedException.prototype.name = 'NotImplementedException';

module.exports = {
  NotImplementedException,
};

In the other files of my project i must have this require line on top of the file.

const Exceptions = require('./exceptions.js');

And to use this error you just need this.

const err = Exceptions.NotImplementedException(`Request token ${requestToken}: The "${operation}" from "${partner}" does not exist.`);

Example of a full method implementation

const notImplemented = (requestToken, operation, partner) => {
  logger.warn(`Request token ${requestToken}: To "${operation}" received from "${partner}"`);
  return new Promise((resolve, reject) => {
    const err = Exceptions.NotImplementedException(`Request token ${requestToken}: The "${operation}" from "${partner}" does not exist.`);
    logger.error(err.message);
    return reject(err);
  });
};