How to validate if input in input field has ASCII characters using express-validator ?

24 Dec, 2021
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 Ascii characters are allowed i.e. there is not allowed any Non-ASCII characters (Ex: ñ). We can also validate these input fields to accept only ASCII characters 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 isAscii() 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 ascii characters.
Filename – index.js
javascript
const express = require('express')const bodyParser = require('body-parser')const {validationResult} = require('express-validator')const repo = require('./repository')const { validateAsciiCharacters } = require('./validator')const formTemplet = require('./form') 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 submit ascii textapp.get('/', (req, res) => {  res.send(formTemplet({}))}) // Post route to handle form submission logic andapp.post(  '/register/ascii',  [validateAsciiCharacters],  async (req, res) => {    const errors = validationResult(req)    if(!errors.isEmpty()){      return res.send(formTemplet({errors}))    }    const {submittedBy, ascii} = req.body    await repo.create({submittedBy, ascii})    res.send('Ascii Characters registered 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'      })    )  }   // 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 – form.js: This file contains logic to show the form to submit Ascii text.
javascript
const getError = (errors, prop) => {  try {    return errors.mapped()[prop].msg  } catch (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'>              <form action='/register/ascii' method='POST'>                            <div>                  <div>                    <label class='label' id='submittedBy'>                      Submitted By                    </label>                  </div>                  <input class='input' type='text'                         name='submittedBy'                         placeholder='SubmittedBy'                         for='submittedBy'>                </div>                <div>                  <div>                    <label class='label' id='ascii'>                      Ascii Characters                    </label>                  </div>                  <input class='input' type='text'                         name='ascii' placeholder='Ascii                         characters' for='ascii'>                  <p class="help is-danger">                    ${getError(errors, 'ascii')}                  </p>                </div>                                 <div>                  <button class='button is-primary'>                    Submit                  </button>                </div>              </form>            </div>          </div>        </div>      </body>    </html>    `}
Filename – validator.js: This file contain all the validation logic(Logic to validate a input field to accept only ascii characters).
javascript
const {check} = require('express-validator')const repo = require('./repository')module.exports = {     validateAsciiCharacters : check('ascii')     // To delete leading and trailing space    .trim()     // Validate minimum length of ascii text    // Optional for this context    .isLength({min:8})    .withMessage('Please submit minimum 8 characters long Ascii text')     // Validate input field to accept only ascii chars    .isAscii()    .withMessage('Must be Ascii characters only') }
Filename – package.json
package.json file
Database:
Database
Output:
Attempt to submit form when Ascii characters input field contains non ascii characters
Response when attempt to submit form where Ascii characters input field contains non ascii characters
Attempt to submit form when Ascii characters input field contains only ascii characters
Response when attempt to submit form where Ascii characters input field contains only ascii characters
Database after successful form submission:
Database after successful form submission
Note: We have used some Bulma classes(CSS framework) in the signup.js file to design the content.
kk773572498
Express.js
Node.js-Misc
Node.js
Web Technologies
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