How to Validate Data using express-validator Module in Node.js ?

Difficulty Level : Expert
Last Updated : 29 Apr, 2020

Validation in node.js can be easily done by using the express-validator module. This module is popular for data validation. There are other modules available in market like hapi/joi, etc but express-validator is widely used and popular among them.

Steps to install express-validator module:

You can install this package by using this command.
```
npm install express-validator
```
After installation, you can check your express-validator module version in command prompt using the command.
```
npm version express-validator
```

After that, you can just create a simple data as shown below to send the data to the server.

Filename: SampleForm.ejs

<!DOCTYPE html>
<html>
    <head>
        <title>Validation using Express-Validator</title>
    </head>
<body>
<h1>Demo Form</h1>
   
<form action="saveData" method="POST">
  <pre>
      Enter your Email    : <input type="text" name="email"> <br>
      Enter your Name     : <input type="text" name="name"> <br>
      Enter your Number   : <input type="number" name="mobile"> <br>
      Enter your Password : <input type="password" name="password"> <br>
      <input type="submit" value="Submit Form"> 
  </pre>
</form>
   
</body>
</html>

After that, you can just create a file, for example index.js as show below:

Filename: index.js

const { check, validationResult }
    = require('express-validator');
  
const bodyparser = require('body-parser')
const express = require("express")
const path = require('path')
const app = express()
  
var PORT = process.env.port || 3000
  
// View Engine Setup
app.set("views", path.join(__dirname))
app.set("view engine", "ejs")
  
// Body-parser middleware
app.use(bodyparser.urlencoded({ extended: false }))
app.use(bodyparser.json())
  
app.get("/", function (req, res) {
    res.render("SampleForm");
})
  
// check() is a middleware used to validate
// the incomming data as per the fields
app.post('/saveData', [
    check('email', 'Email length should be 10 to 30 characters')
                    .isEmail().isLength({ min: 10, max: 30 }),
    check('name', 'Name length should be 10 to 20 characters')
                    .isLength({ min: 10, max: 20 }),
    check('mobile', 'Mobile number should contains 10 digits')
                    .isLength({ min: 10, max: 10 }),
    check('password', 'Password length should be 8 to 10 characters')
                    .isLength({ min: 8, max: 10 })
], (req, res) => {
  
    // validationResult function checks whether
    // any occurs or not and return an object
    const errors = validationResult(req);
  
    // If some error occurs, then this
    // block of code will run
    if (!errors.isEmpty()) {
        res.json(errors)
    }
  
    // If no error occurs, then this
    // block of code will run
    else {
        res.send("Successfully validated")
    }
});
  
app.listen(PORT, function (error) {
    if (error) throw error
    console.log("Server created Successfully on PORT ", PORT)
})

Steps to run the program:

The project structure will look as shown below:
Make sure you have a ‘view engine’. We have used “ejs” and also install express and express-validator, body-parser using following commands:
```
npm install ejs
```
```
npm install express
```
```
npm install body-parser
```
```
npm install express-validator
```
Run index.js file using below command:
```
node index.js
```
Open the browser and type this URL http://localhost:8080/, the fill this sample form with correct data as shown below:
Then submit the form and if no error occurs, then you will see the following output:
And if you try to submit the form with incorrect data, then you will see the error message as shown below:

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