Make sure MongooseError is exported in TypeScript

[kspshnik]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

A tool to detect if error is MongooseError.
The most simple approach is to check if (error instanceof MongooseError). But unfortunately this class is not exported, so one need to check if error is instance of all the exported descendants of it.
The idea is to export a very simple member:

const ifMongooseError = (error: Error) : boolean => error instanceof MongooseError;

This will allow to find out if it's Mongoose's error and do not lead to leaking of private MongooseError class.

Motivation

Sometimes one need to transform thrown by Mongoose and caught in .catch()/catch or passed to errors handler(s) by .catch(next) (if using Express). It would be very nice to have a tool to detect if it's a Mongoose error, since several sources of error might exist in the same controller, like celebrate does (celebrate.isCelebrateError() method).
At present, I use a helper that check against all 16 types of errors. It would be way more refined and elegant to have a built-in Mongoose method.

Example

// ...somewhere in errors handler

elseif (mongoose.isMongooseError(error)) {
 /* Process, transform and/or send to client error */
}

[ramos-ph]

Hey, I was skimming through the code to make sure it was exported, and I found out that it's actually exported as mongoose.Error. Here's a little snippet I made to test things:

// main.ts
import mongoose from 'mongoose';

const UserSchema = new mongoose.Schema({ name: String });
const User = mongoose.model('user', UserSchema);

async function main() {
  try {
    await User.create({ name: 'John Doe' }); // MongooseError: Operation `users.insertOne()` buffering timed out after 10000ms
  } catch (err) {
    console.log(err instanceof mongoose.Error); // true
    console.log((err as Error).name); // MongooseError
  }
}

main();

I ended up finding the definition on those files:

mongoose/lib/error/index.js

Line 51 in c1c3dfe

module.exports = exports = MongooseError;

mongoose/lib/index.js

Line 1142 in c1c3dfe

Mongoose.prototype.Error = require('./error/index');

Making the following export makes err instanceof MongooseError work, but it doesn't seem to have any difference rather than the class name.

// lib/index.js#1143
Mongoose.prototype.MongooseError = require('./error/mongooseError');

I'm just wondering if Error and MongooseError are different in any way. If so, pardon me for the lack of knowledge.

[kspshnik]

I'm just wondering if Error and MongooseError are different in any way. If so, pardon me for the lack of knowledge.

Isn't it actually a Mongo error in your snippet? They're different. I meant Mongoose errors descrbed in docs here: https://mongoosejs.com/docs/api/error.html#Error()

And its not a TS solution anyway %(

[ramos-ph]

I see. I changed my snippet using the example of the docs:

import mongoose from 'mongoose';

const Model = mongoose.model('model', new mongoose.Schema({ answer: Number }));

async function main() {
  const doc = new Model({ answer: 'not a number' });
  const err = doc.validateSync();

  console.log(err instanceof mongoose.Error); // true
  console.log(err instanceof mongoose.MongooseError); // true
  console.log(err instanceof mongoose.Error.ValidationError); // true
}

main();

I'm exporting MongooseError the same way, but I didn't noticed any TypeScript changes when I changed errors.d.ts. I'll update my PR.

[kspshnik]

I'm exporting MongooseError the same way, but I didn't noticed any TypeScript changes when I changed errors.d.ts. I'll update my PR.

It seems to me to be more useful to have an exported helper function in the same way they did it in Celebrate. I mean something like isMoongoseError( error: Error ) : boolean that performs all the required underneath.

[ramos-ph]

It seems to me to be more useful to have an exported helper function in the same way they did it in Celebrate. I mean something like isMoongoseError( error: Error ) : boolean that performs all the required underneath.

It's something that @vkarpov15 suggested on my PR. I originally had implemented a isMongooseError util.
Here's the comment for reference: #13403 (review)

[kspshnik]

It's something that @vkarpov15 suggested on my PR. I originally had implemented a isMongooseError util.

OK, I see.

Thank you!