NodeJS express validation you must know

 

NodeJS express validation you must know

Express is a popular Node.js framework for building web applications and APIs. One important aspect of building web applications is data validation, which is the process of ensuring that user input is in the correct format and meets certain requirements. In this blog post, we will discuss how to perform validation in an Express application using the express-validator library.

First, let's install the express-validator library by running the following command in the terminal:

npm install express-validator

Next, we need to import the library in our Express application and configure it to use the middleware. This is done by adding the following code to our app.js file:

const express = require('express');
const { check, validationResult } = require('express-validator');
const app = express();
app.use(express.json());
app.use(express.urlencoded({ extended: true }));
app.use(express.static(__dirname + '/public'));

The check function is used to specify validation rules for a specific input field. For example, the following code checks that the "name" field is not empty and has a maximum length of 50 characters:

app.post('/register', [
    check('name').not().isEmpty().withMessage('Name is required').isLength({ max: 50 }).withMessage('Name must be less than 50 characters'),
    check('email').isEmail().withMessage('Invalid email'),
    check('password').isLength({ min: 8 }).withMessage('Password must be at least 8 characters')
], (req, res) => {
    const errors = validationResult(req);
    if (!errors.isEmpty()) {
        return res.status(400).json({ errors: errors.array() });
    }
    // If validation passes, process the form...
});

In this example, we are using the "post" method to handle the registration form submission. Inside the callback function, we use the validationResult function to check for any validation errors. If there are any errors, we return a response with a 400 status code and a JSON object containing the error messages.

It's also possible to chain multiple validation rules together, like in the example above.

We can also use custom validation functions by passing a function to the check method. For example, we can check that a password field matches a confirm password field by adding the following code:

app.post('/register', [
    check('password').isLength({ min: 8 }).withMessage('Password must be at least 8 characters'),
    check('confirm_password').custom((value, { req }) => {
        if (value !== req.body.password) {
            throw new Error('Password confirmation does not match password');
        }
        return true;
    })
], (req, res) => {
    const errors = validationResult(req);
    if (!errors.isEmpty()) {
        return res.status(400).json({ errors: errors.array() });
    }
    // If validation passes, process the form...
});

In this example, we are using the custom method to compare the value of the "confirm_password" field with the value of the "password" field. If the values do not match, we throw an error.

In conclusion, the express-validator library is a powerful tool for performing validation in an Express application