How to validate if input in input field is divisible by or multiple of a number 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, only numbers that are multiples of a particular number are allowed i.e. there not allowed any letters, special characters, or a number that is not multiple of a particular number. We can also validate these input fields to accept only those particular 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 isDivisibleBy(number) with ‘ . ‘
- Sanitize the input to convert it from string to integer by chaining on the sanitization method toInt() 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 only allow numbers those are divisible by some particular number.
Filename – index.js
javascript
const express = require( 'express' ) const bodyParser = require( 'body-parser' ) const {validationResult} = require( 'express-validator' ) const repo = require( './repository' ) const { validateAmount } = 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' , [validateAmount], async (req, res) => { const errors = validationResult(req) if (!errors.isEmpty()){ return res.send(formTemplet({errors})) } const {name, ano, pin, amount} = req.body // New record await repo.create({ 'Account Name' :name, 'Account Number' :ano, 'Secret Password' :pin, 'Amount' :amount, }) res.send( '<strong>Transaction successful!</strong>' ) }) // Server set to run 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
// 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 format. 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= '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= '/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= 'ano' > Account number </label> </div> <input class= 'input' type= 'text' name= 'ano' placeholder= 'Account Nnumber' for = 'ano' > </div> <div> <div> <label class= 'label' id= 'pin' > Secret Password </label> </div> <input class= 'input' type= 'text' name= 'pin' placeholder= 'XXXXXX' for = 'pin' > </div> <div> <div> <label class= 'label' id= 'amount' > Amount </label> </div> <input class= 'input' type= 'text' name= 'amount' placeholder= 'Amount in multiple of 100' for = 'amount' > <p class= "help is-danger" > ${getError(errors, 'amount' )} </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 uppercase letters).
javascript
const {check} = require( 'express-validator' ) const repo = require( './repository' ) module.exports = { validateAmount : check( 'amount' ) // To delete leading and trailing space .trim() // Convert amount to integer from string .toInt() // Validate name to accept only a // number divisible by 'num' .isDivisibleBy(100) // Custom message .withMessage( 'Must be multiple of 100' ) } |
Filename – package.json
Database:
Output:
Database after successful form submission:
Note: We have used some Bulma classes(CSS framework) in the form.js file to design the content.