Mongoose - Why we make “mongoose.Promise = global.Promise” when setting a mongoose module?

Question

I\'m working with Mongoose. I have seen a lot of developers make the following command:

mongoose.Promise = global.Promise;

Then I was curi

Answer 1

This is legacy code from older examples that isn't needed with Mongoose 5.

Mongoose 4 relied on its own promise implementation, mpromise. mongoose.Promise wasn't necessarily Promise global.

As Mongoose 4 documentation states:

Mongoose 5.0 will use native promises by default (or bluebird, if native promises are not present) but still support plugging in your own ES6-compatible promises library. Mongoose 5.0 will not support mpromise.

Though the statement about Bluebird is no longer true; Mongoose 5 dropped the support of Node versions that don't have native promises.

mongoose.Promise = global.Promise;

may still be needed if global.Promise was assigned with another implementation (e.g. Bluebird) after Mongoose was imported, though a better thing would be to assign global.Promise = Bluebird earlier instead.