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How to compare password and confirm password inputs using express-validator ?

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The registration or Sign Up in any website always requires a confirm password input and it must be the same as the password. It is basically to ensure that the user enters the password full of his sense and there is no conflict happens. This functionality can be implemented anywhere in our code like in index file or route file but this comes under the validation part. So we usually prefer to code this logic where all the other validations are coded. Here we use ‘express-validator’ middleware to implement this functionality.

Command to install express-validator

npm install express-validator

Steps to use express-validator to implement the logic:

  • Install express-validator middleware.
  • Create a validator.js file to code all the validation logic.
  • Validate confirmPassword by validateConfirmPassword: check(‘confirmPassword’) and chain on all the validation with ‘ . ‘
  • Use the validation name(validateConfirmPassword) in the routes as a middleware as an array of validations.
  • Destructure ‘validationResult’ function from express-validator to use it to find any errors
  • If error occurs redirect to the same page passing the error information
  • If error list is empty, give access to the user for the subsequent request.

Note: Here we use local or custom database to implement the logic, the same steps can be followed to implement the logic in a regular database like MongoDB or MySql.

Example 1: This example illustrates how to check if email address is already in use or not for a particular website.


Filename: index.js



const express = require('express')
const bodyParser = require('body-parser')
const {validationResult} = require('express-validator')
const repo = require('./repository')
const { validateConfirmPassword } = require('./validator')
const signupTemplet = require('./signup')
const app = express()
const port = process.env.PORT || 3000
// The body-parser middleware to parse form data
app.use(bodyParser.urlencoded({extended : true}))
// Get route to display HTML form to sign in
app.get('/signup', (req, res) => {
// Post route to handle form submission logic and
  async (req, res) => {
    const errors = validationResult(req)
      return res.send(signupTemplet({errors}))
    const {email, password} = req.body
    await repo.create({email, password})
    res.send('Sign Up successfully')
// Server setup
app.listen(port, () => {
  console.log(`Server start on port ${port}`)

Filename: repository.js This file contains all the logic to create a local database and interact with it. 


// Importing node.js file system module
const fs = require('fs')
class Repository {
    constructor(filename) {
        // The filename where datas are
        // going to store
        if (!filename) {
            throw new Error(
'Filename is required to create a datastore!')
        this.filename = filename
        try {
        } catch (err) {
            // If file not exist it is
            // created with empty array
            fs.writeFileSync(this.filename, '[]')
    // Get all existing records
    async getAll() {
        return JSON.parse(
            await fs.promises.readFile(this.filename, {
                encoding: 'utf8'
    // Find record by properties
    async getOneBy(filters) {
        const records = await this.getAll()
        for (let record of records) {
            let found = true
            for (let key in filters) {
                if (record[key] !== filters[key]) {
                    found = false
            if (found) return record;
    // Create new record
    async create(attrs) {
        const records = await this.getAll()
        await fs.promises.writeFile(
            JSON.stringify(records, null, 2)
        return attrs
// The 'datastore.json' file created at runtime
// and all the information provided via signup form
// store in this file in JSON format.
module.exports = new Repository('datastore.json')

Filename: signup.js This file contains logic to show sign up form. 


const getError = (errors, prop) => {
    try {
        return errors.mapped()[prop].msg
    } catch (error) {
        return ''
module.exports = ({ errors }) => {
    return `
      <!DOCTYPE html>
          <link rel='stylesheet'
              margin-top: 100px;
              margin-top : 10px
      <div class='container'>
        <div class='columns is-centered'>
          <div class='column is-5'>
            <h1 class='title'>Sign Up<h1>
            <form method='POST'>            
                 <label class='label' id='email'>
                <input class='input' type='text'
                placeholder='Email' for='email'>
                  <label class='label' id=
                <input class='input' type=
                    'password' name='password'
                placeholder='Password' for='password'>
                 <label class='label' id='confirmPassword'>
                    Confirm Password</label>
                <input class='input' type='password'
                placeholder='Confirm Password'
                <p class="help is-danger">
                    ${getError(errors, 'confirmPassword')}
                <button class='button is-primary'>
                    Sign Up</button>

Filename: validator.js This file contain all the validation logic (Logic to see if password and passwordConfirm are same). 


const {check} = require('express-validator')
const repo = require('./repository')
module.exports = {
  validateConfirmPassword : check('confirmPassword')
    // To delete leading and trailing space
    // Validate minimum length of password
    // Optional for this context
    .isLength({min:4, max:16})
    // Custom message
    .withMessage('Password must be between 4 to 16 characters')
    // Custom validation
    // Validate confirmPassword
    .custom(async (confirmPassword, {req}) => {
      const password = req.body.password
      // If password and confirm password not same
      // don't allow to sign up and throw error
      if(password !== confirmPassword){
        throw new Error('Passwords must be same')

Filename: package.json

package.json file




Attempt to sign up when password and confirm password inputs are different

Response when attempt to sign up with different password and confirm password inputs

Attempt to sign up when password and confirm password inputs are same

Response when attempt to sign up with same password and confirm password inputs

Database after successful Sign Up(Sign Up with same password and confirm password inputs)

Database after successful Sign Up(Sign Up with same password and confirm password inputs)

Note: We have used some Bulma classes(CSS framework)  in the signup.js file to design the content.

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Last Updated : 14 Jan, 2022
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