How to validate if input in input field must contains a seed word using express-validator ?

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, we often need to validate input so that it must contain a seed word i.e. input can be anything(any string) but must contain a particular word(seed word). We can also validate these input fields to accept only those values that contain the seed word 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 validation contains(seed) with ‘ . ‘
  • If want to ignore the case sensitivity add options object argument {ignoreCase:true}. By default ignoreCase set to true.
  • 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 only allow the values that contains the seed word.



Filename – index.js

filter_none

edit
close

play_arrow

link
brightness_4
code

const express = require('express')
const bodyParser = require('body-parser')
const {validationResult} = require('express-validator')
const repo = require('./repository')
const { validatePlayerName } = 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) => {
  res.send(formTemplet({}))
})
  
// Post route to handle form submission logic and 
app.post(
  '/info',
  [validatePlayerName],
  async (req, res) => {
    const errors = validationResult(req)
      
    if(!errors.isEmpty()) {
      return res.send(formTemplet({errors}))
    }
      
    const {name, dept, event, pname} = req.body
  
    // New record
    await repo.create({
      'Name':name,
      'Department':dept,
      'Event Name':event,
      'Player Name':pname,
    })
    res.send(
'<strong>Registered Successfully for the event!!</strong>')
})
  
// Server setup
app.listen(port, () => {
  console.log(`Server start on port ${port}`)
})

chevron_right


Filename – repository.js: This file contains all the logic to create a local database and interact with it.

filter_none

edit
close

play_arrow

link
brightness_4
code

// Importing node.js file system module 
const fs = require('fs')
  
class Repository {
  
  constructor(filename) {
  
    // 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) {
    // Fetch all existing records
    const records = await this.getAll()
  
    // All the existing records with new 
    // record push back to database
    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 formet.
module.exports = new Repository('datastore.json')

chevron_right


Filename – form.js: This file contains logic to show the form to submit the data.

filter_none

edit
close

play_arrow

link
brightness_4
code

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=
  <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='/info' method='POST'>
          <div>
            <div>
              <label class='label' id='name'>
                Name
              </label>
            </div>
            <input class='input' type='text' 
              name='name' placeholder='Vinit singh'
              for='name'>
          </div>
          <div>
            <div>
              <label class='label' id='dept'>
                Department
              </label>
            </div>
            <input class='input' type='text' 
              name='dept' placeholder='Department' 
              for='dept'>
          </div>
          <div>
            <div>
              <label class='label' id='event'>
                Event Name
              </label>
            </div>
            <input class='input' type='text' 
              name='event' placeholder='Event Name' 
              for='event'>
          </div>
          <div>
            <div>
              <label class='label' id='pname'>
                Player Name
              </label>
            </div>
            <input class='input' type='text' name='pname' 
              placeholder=
              "Player Name must contains the word 'jolite'"
              for='pname'>
            <p class="help is-danger">
              ${getError(errors, 'pname')}
            </p>
          </div>
          <div>
            <button class='button is-primary'>
              Submit
            </button>
          </div>
        </form>
      </div>
    </div>
  </div>
</body>
  
</html>
  `
}

chevron_right


Filename – validator.js: This file contain all the validation logic (Logic to validate an input field to only allow the value that contains the seed word).

filter_none

edit
close

play_arrow

link
brightness_4
code

const {check} = require('express-validator')
const repo = require('./repository')
module.exports = {
    
  validatePlayerName : check('pname')
  
    // To delete leading and triling space
    .trim()
  
    // Validate player name to accept only
    // the string that contains the word 'jolite'
    // ignorecase is an optional attribute 
    // and it is by default set to false if 
    // ignorecase attribute set to be true, 
    // it ignores the case sensitivity 
    // of the required seed word
    .contains('jolite', { ignoreCase: true})
  
    // Custom message
    .withMessage(
"Player Name must contains the word 'jolite'")   
}

chevron_right


Filename – package.json

package.json file

Database:

Database

Output:

Attempt to submit form data when player name input field not  contains the seed word ‘jolite’


Response when attempt to submit form data where player name input field not  contains the seed word ‘jolite’


Attempt to submit form data when player name input field  contains the seed word ‘jolite’


Attempt to submit form data when player name input field  contains the seed word ‘jolite'(in capital letter)


Response when attempt to submit form data where player name input field contains the seed word ‘jolite’

Database after successful submission of form:

Database after successful submission of form

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




My Personal Notes arrow_drop_up

Recommended Posts:


Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.