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

08 Apr, 2022
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
javascript
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 dataapp.use(bodyParser.urlencoded({ extended: true })) // Get route to display HTML form to sign upapp.get('/signup', (req, res) => {    res.send(signupTemplet({}))}) // Post route to handle form submission logic andapp.post(    '/signup',    [validateEmail],    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 setupapp.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.
javascript
// Importing node.js file system moduleconst 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 {            fs.accessSync(this.filename)        } 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()        records.push(attrs)        await fs.promises.writeFile(            this.filename,            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.
javascript
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>      <html>        <head>          <link rel='stylesheet'href='https://cdnjs.cloudflare.com/ajax/libs/bulma/0.9.0/css/bulma.min.css'>          <style>            div.columns{              margin-top: 100px;            }            .button{              margin-top : 10px            }          </style>        </head>        <body>          <div class='container'>            <div class='columns is-centered'>              <div class='column is-5'>                <h1 class='title'>Sign Up<h1>                <form method='POST'>                              <div>                    <div>                      <label class='label'                        id='email'>Username</label>                    </div>                    <input class='input' type='text'                        name='email' placeholder='Email'                        for='email'>                    <p class="help is-danger">                        ${getError(errors, 'email')}                    </p>                  </div>                  <div>                    <div>                        <label class='label' id='password'>                            Password                        </label>                    </div>                    <input class='input' type='password'                    name='password' placeholder='Password'                            for='password'>                  </div>                  <div>                    <button class='button is-primary'>                        Sign Up                    </button>                  </div>                </form>              </div>            </div>          </div>        </body>      </html>      `}
Filename: validator.js This file contain all the validation logic (Logic to see if email already exist or not).
javascript
const { check } = require('express-validator')const repo = require('./repository') module.exports = {     validateEmail: check('email')         // To delete leading and triling space        .trim()         // Normalizing the email address        .normalizeEmail()         // Checking if follow the email        // address format or not        .isEmail()         // 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
Database:
Database
Output:
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.
rkbhola5
Node.js-Misc
Node.js
Web Technologies
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