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How to validate if input in input field has BIC or Swift code only using express-validator ?

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  • Last Updated : 30 Jul, 2020
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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. When working with a bank system, In a certain input field only a valid Bank identification code(BIC) is allowed. BIC is an 8 or 11 digit string. It represents a valid bank with its location uniquely. We can also validate these input fields to accept only valid BIC using express-validator middleware.

Condition to be a valid BIC:

  • Bank Code: 4 letter code and only upper case alphabets are allowed.
  • Country Code: 2 letter code and only upper case alphabets are allowed.
  • Location Code: 2 letter code, either digits (0 to 9) or upper case alphabets are allowed.
  • Branch Code: 3 letter optional code, either digits (0 to 9) or upper case alphabets are allowed.

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 isBIC() 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 a input field to accept only valid BIC.

Filename – index.js

const express = require('express')
const bodyParser = require('body-parser')
const {validationResult} = require('express-validator')
const repo = require('./repository')
const { validateBic } = require('./validator')
const formTemplet = require('./form')
const showTemplet = require('./show')
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 {aNumber, bic} = req.body
    const account = await repo.getOneBy({
      'accountNumber': aNumber,
      'bic': bic
      res.send('<strong>Account Not Found</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
      fs.writeFileSync(this.filename, '[]')
  // Get all existing records
  async getAll(){
    return JSON.parse(
      await fs.promises.readFile(this.filename, {
        encoding : 'utf8'
  // Find record by property
  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;
// 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 the form to fetch bank Information.

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='/account' method='POST'>             
                    <label class='label' id='aNumber'>
                      Account Number
                  <input class='input' type='text' name='aNumber' 
                  placeholder='Account Number' for='aNumber'>
                  <label class='label' id='bic'>
                    Bank Identification Code
                 <input class='input' type='text' name='bic' 
                 placeholder='BIC' for='bic'>
                 <p class="help is-danger">
                   ${getError(errors, 'bic')}
                  <button class='button is-primary'>

Filename – show.js: This file contains logic to show the fetched bank information.

module.exports = (account) => {
  return `
        <strong>Account Name :</strong>
        <strong>Account Number :</strong>
        <strong>Account Type :</strong>
        <strong>BIC :</strong>
        <strong>Bank Name :</strong>
        <strong>Bank Location :</strong>

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

const {check} = require('express-validator')
const repo = require('./repository')
module.exports = {
  validateBic : check('bic')
    // To delete leading and trialing space
    // Validate input field to accept only BIC
    .withMessage('Must be a valid Bank identification code')

Filename – package.json

package.json file




Invalid first two digit(Only Alphabets allowed)

Invalid 3rd and 4th digit(Only Alphabets allowed)

Invalid 5th and 6th digit(Only Alphabets allowed)

Response when submit invalid BIC(In first three cases)

valid BIC

Response when submit valid BIC

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

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