How does Query.prototype.cursor() work in Mongoose?

The Query.prototype.cursor() function returns a wrapper around a MongoDB driver cursor. And this function triggers the pre find hooks, not the post find hooks.
Syntax:

Query.prototype.cursor()

Parameters: This function has one optional parameter i.e. transform which is an optional function which accepts a mongoose document.
Return Value: This function returns QueryCursor Object.
Installing mongoose : 

npm install mongoose

After installing the mongoose module, you can check your mongoose version in command prompt using the command. 

npm mongoose --version

Now, create a folder and add a file for example, index.js as shown below.

Database: The sample database used here is shown below:

Example 1:

index.js

const mongoose = require('mongoose');

// Database connection
mongoose.connect('mongodb://127.0.0.1:27017/geeksforgeeks', {
    useNewUrlParser: true,
    useCreateIndex: true,
    useUnifiedTopology: true
});

// User model
const User = mongoose.model('User', {
    name: { type: String },
    age: { type: Number }
});

var cursor = User.find({}).cursor();

cursor.next(function(error, doc) {
  console.log(doc);
});

Steps to run the program:

The project structure will look like this: 

Run index.js file using below command: 

node index.js

Output:

{ _id: 5ebb9129a99bde77b2efb809, name: ‘Gourav’, age: 10, __v: 0 }

Example 2:

index.js

const express = require('express');
const mongoose = require('mongoose');
const app = express()

// Database connection
mongoose.connect('mongodb://127.0.0.1:27017/geeksforgeeks', {
    useNewUrlParser: true,
    useCreateIndex: true,
    useUnifiedTopology: true
});

// User model
const User = mongoose.model('User', {
    name: { type: String },
    age: { type: Number }
});

var cursor = User.find({}).cursor();

//first call
cursor.next(function(error, doc) {
  console.log(doc);
});

//second call
cursor.next(function(error, doc) {
  console.log(doc);
});

//third call
cursor.next(function(error, doc) {
    console.log(doc);
});

app.listen(3000, function(error ) {
    if(error) console.log(error)
    console.log("Server listening on PORT 3000")
});

Steps to run the program:

The project structure will look like this: 

Run index.js file using below command: 

node index.js

Output:

Server listening on PORT 3000
{ _id: 5ebb9129a99bde77b2efb809, name: ‘Gourav’, age: 10, __v: 0 }
{ _id: 5ebc3669a99bde77b2efb9ba, name: ‘Lalit’, age: 25, __v: 0 }
{ _id: 5ebc367da99bde77b2efb9bf, name: ‘Piyush’, age: 5, __v: 0 }

Reference:
https://mongoosejs.com/docs/api/query.html#query_Query-cursor