ObjectId valueOf not working

[m-weeks]

Do you want to request a feature or report a bug?
bug

What is the current behavior?
checking equality of two ObjectIds with the same ID is always false.

When I run myObjectId.valueOf() it appears to output a new ObjectId instead of the string representation like expected.

If the current behavior is a bug, please provide the steps to reproduce.

var mongoose = require('mongoose');
var ObjectId = mongoose.Types.ObjectId;

var a = new ObjectId('6143b55ac9a762738b15d4f0');
var b = new ObjectId('6143b55ac9a762738b15d4f0');

console.log(a == b); // false
console.log(a.valueOf() == b.valueOf()); // false

I believe the issue is due to this check:

if (ObjectId.prototype.valueOf === void 0) {
  ObjectId.prototype.valueOf = function objectIdValueOf() {
    return this.toString();
  };
}

When I run the ObjectId.prototype.valueOf === void 0 on the mongodb driver ObjectId it's false, so I believe the overridden function isn't being applied.

What is the expected behavior?
According to the 6.0 Migration document:

ObjectId valueOf()
Mongoose now adds a valueOf() function to ObjectIds. This means you can now use == to compare two ObjectId instances.

Although this doesn't seem to be the case.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
Node: 12.16
Mongoose: 6.0.6
MongoDb: 4.4

[IslandRhythms]

const mongoose = require('mongoose');
const ObjectId = mongoose.Types.ObjectId;

const a = ObjectId('6143b55ac9a762738b15d4f0');
const b = ObjectId('6143b55ac9a762738b15d4f0');

console.log(a == b);
console.log(a.valueOf() == b.valueOf());

[vkarpov15]

Re: valueOf() returning an object, that's a bug and we'll fix it for v6.0.8.

Re: the claim that "you can now use == to compare two ObjectId instances", that's unfortunately also wrong. Two objects cannot be == each other without being the same reference. Equality in JavaScript is pretty strict about that. But what you should be able to do now is compare an object id against a string:

const mongoose = require('mongoose');
const ObjectId = mongoose.Types.ObjectId;

const a = ObjectId('6143b55ac9a762738b15d4f0');

a == '6143b55ac9a762738b15d4f0'; // true

[mohd-akram]

It seems mongodb's ObjectId already supports this, and it also has an .equals method for comparing two ids, so it seems overriding valueOf is not necessary.

const a = new require('mongodb').ObjectId();
console.log(a == a.toString());