CODE EXAMPLE FOR JAVASCRIPT

create auto increment mongodb mongoose

// using pre('save' on your mongoose schema

// creating the counter collection/model to save the number of documents:
const counterCollection = mongoose.model('counter',
	new mongoose.Schema({number: Number}), 'counter')

// updating the counter and the pre-saved document that need the index/number
documentSchema.pre('save', async function() {
  if(this.number) {
    let counterDoc = await counterCollection.findOne()
    if(!counterDoc) {
      counterDoc = new counterCollection({number: 1})
    } else {
      counterDoc.number++
    }
    this.number = counterDoc.number
    const response = await counterDoc.save()
  }
})
// don't forget to update the schema with the number key-value pair to
// store the number, so mongoose does not throw error