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How to check if email address is already in use or not using express-validator in Node.js ?

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  • Last Updated : 08 Apr, 2022
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The registration or Sign Up in any website always requires a username. Most of the time we use ’email’ to register on a website. The registration email is always unique and must refer to only one user otherwise conflict between the users can happen. To solve this conflict every website must have the functionality to not accept the email that already exists on the website. 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 email by validateEmail : check(’email’) and chain on all the validation with ‘ .
  • Use the validation name(validateEmail) 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: 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 { validateEmail } = 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 up
app.get('/signup', (req, res) => {
// Post route to handle form submission logic and
    async (req, res) => {
        const errors = validationResult(req)
        if (!errors.isEmpty()) {
            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 error message if any error occurs
        return errors.mapped()[prop].msg
    } catch (error) {
        // Return empty string if no 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'
                    <input class='input' type='text'
                        name='email' placeholder='Email'
                    <p class="help is-danger">
                        ${getError(errors, 'email')}
                        <label class='label' id='password'>
                    <input class='input' type='password'
                    name='password' placeholder='Password'
                    <button class='button is-primary'>
                        Sign Up

Filename: validator.js This file contain all the validation logic (Logic to see if email already exist or not).


const { check } = require('express-validator')
const repo = require('./repository')
module.exports = {
    validateEmail: check('email')
        // To delete leading and triling space
        // Normalizing the email address
        // Checking if follow the email
        // address format or not
        // Custom message
        .withMessage('Invalid email')
        // Custom validation
        // Validate email in use or not
        .custom(async (email) => {
            const existingUser =
                await repo.getOneBy({ email })
            if (existingUser) {
                throw new Error('Email already in use')

Run index.js file using the following command:

node index.js

Filename: package.json

package.json file




Sign Up with email already in use

Response when Sign Up with email that already in use

Sign Up with email that not in use

Response when Sign Up with email that not in use

Database after successful Sign Up(Sign Up with email that not in use)

Database after successful Sign Up(Sign Up with email that not in use)

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

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