[{"id":1,"name":"A","createdOn":ISODate("2021-07-13")},{"id":2,"name":"B","createdOn":ISODate("2021-08-02")},{"id":3,"name":"C","createdOn":ISODate("2021-08-15")},{"id":4,"name":"D","createdOn":ISODate("2021-09-07")},{"id":5,"name":"E","createdOn":ISODate("2021-09-12")},]

db.collection.find({$where:"function() { var currentDate = new Date(); var lastMonthDate = new Date(currentDate.setMonth(currentDate.getMonth() - 1)); return this.createdOn.getFullYear() === lastMonthDate.getFullYear() && this.createdOn.getMonth() === lastMonthDate.getMonth(); }"})