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

The Query.prototype.batchSize() is used to set the batchSize option. The batchSize() function basically instructs the driver to retrieve a certain number of items per time.
Syntax:

Query.prototype.batchSize()

Parameters: This function has one array parameter i.e. number defining the batch size.
Return Value: This function returns Query 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

After that, you can just create a folder and add a file for example, index.js as 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 }
});

const query = User.find();
query.batchSize(100);

console.log("The batch size set is :", query.options)

The project structure will look like this:

Run index.js file using below command: 

node index.js

Output:

The batch size set is : { batchSize: 100 }

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 }
});

const query = User.find();
query.batchSize(140);

console.log("Batch Size defined is:", query.options)

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

The project structure will look like this:

Run index.js file using below command: 

node index.js

Output:

Server listening on PORT 3000
Batch Size defined is: 140

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