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How to validate if input in input field has base 32 encoded string using express-validator ?

Last Updated : 21 Mar, 2023
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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. If In a certain input field, only base 32 encoded strings are allowed i.e. there not allowed any other form of string which does not constitute base32 encoded string. We can also validate these input fields to accept only base 32 encoded strings 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 isBase32() 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 base 32 encoded string.

Filename – index.js


const express = require('express')
const bodyParser = require('body-parser')
const { validationResult } = require('express-validator')
const repo = require('./repository')
const { validateBase32Data } = 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)
        if (!errors.isEmpty()) {
            return res.send(formTemplet({ errors }))
        const { name, base32data } = req.body
        await repo.create({
        res.send('<h2>Base 32 data decoded and Stored'
            + ' successfully in the database</h2>')
// 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')
const base32Decode = require('base32-decode')
let ab2str = require('arraybuffer-to-string')
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'
    // Create new record
    async create(attrs) {
        const records = await this.getAll()
        // Decoding base 32 encoded string
        const arrayBuff = base32Decode(
            attrs.base32data, 'RFC4648')
        // The uint8 array raw form of decoded string
        const uint8 = new Uint8Array(arrayBuff)
        // The uint8 array raw form to string
        const data = ab2str(uint8)
        const record = {
        await fs.promises.writeFile(
            JSON.stringify(records, null, 2)
        return record
// 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.


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='name'>Name</label>
                  <input class='input' type='text' name='name'
                  placeholder='Submitted By' for='name'>
                    <label class='label' id='base32data'>
                      Base 32 data
                  <input class='input' type='text'
                         placeholder='Base 32 Encode data'
                  <p class="help is-danger">
                    ${getError(errors, 'base32data')}
                  <button class='button is-primary'>

Filename – validator.js: This file contains all the validation logic(Logic to validate an input field to accept only base encoded 32 string).


const { check } = require('express-validator')
const repo = require('./repository')
module.exports = {
    validateBase32Data: check('base32data')
        // To delete leading and trailing space
        // Validate input field to accept only base32 string
        // Custom message
        .withMessage('Must be a Base 32 encoded string')

Filename – package.json

package.json file



Online website that converts a normal string to a base 32 string:

Online website that convert a normal string to base 32 string(to show for which string we give base32 input)


Attempt to submit with invalid base32 string

Response when attempt to submit with invalid base 32 string

Response when attempt to submit with invalid base 32 string

Response when attempt to submit with valid base 32 string

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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