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How to validate if input in input field has boolean value using express-validator ?

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  • Last Updated : 24 Dec, 2021
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In HTML forms, we often required validation of different types. Validate existing email, validate password length, validate confirm password, validate to allow only integer inputs, these are some examples of validation. In a certain input field, only boolean value i.e. true or false are allowed. We can also validate these input fields to accept only boolean values using express-validator middleware.

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 input by validateInputField: check(input field name) and chain on the validation isBoolean() with ‘ . ‘
  • Use the validation name(validateInputField) 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 validate an input field to accept only boolean values.

Filename – index.js


const express = require('express')
const bodyParser = require('body-parser')
const {validationResult} = require('express-validator')
const repo = require('./repository')
const { validateCitizenship } = require('./validator')
const formTemplet = require('./form')
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
app.get('/', (req, res) => {
// Post route to handle form submission logic and
  async (req, res) => {
    const errors = validationResult(req)
      return res.send(formTemplet({errors}))
    const {email, name, citizen} = req.body
    await repo.create({
      'Indian Citizen': citizen
    res.send('<strong>Data Stored successfully</strong>')
// 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
  // Get all existing records
  async getAll(){
    return JSON.parse(
      await fs.promises.readFile(this.filename, {
        encoding : 'utf8'
  // 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 – form.js: This file contains logic to show HTML form to submit the data.


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'>
              <form action='/data' method='POST'>
                    <label class='label' id='email'>Email</label>
                  <input class='input' type='text' name='email'
                  placeholder='Email' for='email'>
                    <label class='label' id='name'>Name</label>
                  <input class='input' type='text' name='name'
                  placeholder='Name' for='name'>
                  <label class='label' id='name'>
                    You are citizen of India
                  <input class='input' type='text' name='citizen'
                  placeholder='true or false' for='citizen'>
                  <p class="help is-danger">
                    ${getError(errors, 'citizen')}
                  <button class='button is-primary'>

Filename – validator.js: This file contain all the validation logic(Logic to validate a input field to accept only boolean values).


const {check} = require('express-validator')
const repo = require('./repository')
module.exports = {
  validateCitizenship : check('citizen')
    // To delete leading and trailing space
    // Validate input field to accept only boolean values
    .withMessage('Must be a boolean true or false')

Filename – package.json

package.json file




Invalid boolean value(true is boolean not True)

Invalid boolean value(false is boolean not False)

Invalid boolean value

Response when attempt to submit the form with invalid boolean value (In first three cases)

Valid boolean value

Valid boolean value

Response when attempt to submit the form with valid boolean(true or false) value – (In last two cases)

Database after successful submission of form:

Database after successful submission of form

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

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