Mongoose create a new object within a static function
When you first call the static function this is bound to the model for the schema. You can just do something like this:
someSchema.static('foo', function() { const newUser = new this({ username: username, password: password, }); newUser.save(cb);})Don't replace the anonymous function with a fat arrow equivalent (I know you want to!). this won't have the correct scope.