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

The Query.prototype.mod() function is used to specify a $mod condition. This function basically filters documents for documents whose path property is a number that is equal to remainder modulo divisor.
 

Syntax:  

Query.prototype.mod()

Parameters: This function has one optional path parameter and an array parameter which must be of length 2 where the first element is the divisor and the second element is the remainder.
Return Value: This function returns Query Object. Mongoose Installation:

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.

Database: The sample database used here is shown below: 
 

Example 1:

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().mod('age', [2, 0]);

query.exec(function(err, res){
    if(err) console.log(err)
    else console.log(res)
});

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 },
  { _id: 5ebd345f5d2d8a3534b2f391, name: 'Manish', age: 34, __v: 0 }
]

Example 2:

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().mod('age', [2, 1]);

query.exec(function(err, res){
    if(err) console.log(err)
    else console.log(res)
});

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
[
  { _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-mod