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 integer numbers are allowed i.e. there not allowed any strings, special characters, or anything other than integer number. We can also validate these input fields to accept only integer numbers 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 isInt() 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 only allow integer numbers.
Filename – index.js
javascript
const express = require('express')
const bodyParser = require('body-parser')
const {validationResult} = require('express-validator')
const repo = require('./repository')
const { validateYearOfBirth } = require('./validator')
const formTemplet = require('./form')
const app = express()
const port = process.env.PORT || 3000
app.use(bodyParser.urlencoded({extended : true}))
app.get('/', (req, res) => {
res.send(formTemplet({}))
})
app.post(
'/info',
[validateYearOfBirth],
async (req, res) => {
const errors = validationResult(req)
if(!errors.isEmpty()) {
return res.send(formTemplet({errors}))
}
const {name, qual, ybirth} = req.body
await repo.create({
'Name':name,
'Last Qualification':qual,
'Year of birth':ybirth
})
res.send(
'<strong>Information saved successfully!</strong>')
})
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.
javascript
const fs = require('fs')
class Repository {
constructor(filename) {
if(!filename) {
throw new Error(
'Filename is required to create a datastore!')
}
this.filename = filename
try {
fs.accessSync(this.filename)
} catch(err) {
fs.writeFileSync(this.filename, '[]')
}
}
async getAll(){
return JSON.parse(
await fs.promises.readFile(this.filename, {
encoding : 'utf8'
})
)
}
async create(attrs){
const records = await this.getAll()
records.push(attrs)
await fs.promises.writeFile(
this.filename,
JSON.stringify(records, null, 2)
)
return attrs
}
}
module.exports = new Repository('datastore.json')
|
Filename – form.js: This file contains logic to show the form to submit the data.
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=
<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='qual'>
Last Qulification
</label>
</div>
<input class='input' type='text' name='qual'
placeholder='Ex-B.Tech' for='qual'>
</div>
<div>
<div>
<label class='label' id='ybirthirate'>
Year of Birth
</label>
</div>
<input class='input' type='text' name='ybirth'
placeholder='Ex-1997' for='ybirth'>
<p class="help is-danger">
${getError(errors, 'ybirth')}
</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 only allow the integer numbers).
javascript
const {check} = require('express-validator')
const repo = require('./repository')
module.exports = {
validateYearOfBirth : check('ybirth')
.trim()
.isInt()
.withMessage('Must be a integer number')
}
|
Filename – package.json
Package.json file
Database:
database
Output:
Attempt to submit form data when date of year input field is not a valid integer number
Attempt to submit form data when date of year input field is not a valid integer number
Response when attempt to submit form data where date of year input field is not a valid integer number
Attempt to submit form data when date of year input field is a valid integer number
Response when attempt to submit form data where date of year input field is a valid integer number
Database after successful form submission:
Database after successful submission of form
Note: We have used some Bulma classes(CSS framework) in the form.js file to design the content.