In the world of web development, one of the most important aspects is data validation. This is especially true when dealing with incoming data (say, a POST request), where the security and reliability of your application depend on the quality of the data you receive. In this blog post, I'll explore how to validate incoming data in Express.js using the Ajv library, and why it's essential to do so.

What is Ajv?

Ajv is a powerful JSON schema validator that is easy to use and highly configurable. It's a popular choice for developers working with JSON data and comes with a range of features that make it an excellent tool for validating incoming data in Express.js applications. One of the key benefits of using Ajv is that it helps you catch errors in your data early on, which can save you time and money in the long run.

Why validate incoming data?

There are several reasons why you should validate incoming data in your Express.js application. First and foremost, it ensures that your application is receiving the correct data and that it is formatted correctly. This is important because it prevents your application from crashing due to unexpected data input.

Secondly, validating incoming data ensures the security of your application. By checking that the data you receive is safe and formatted correctly, you can prevent attackers from exploiting vulnerabilities in your application. In other words, data validation helps you to maintain the integrity of your application, protecting both your users and your business.

How to validate incoming data in Express.js using Ajv?

Let's take a look at how to validate data in Express.js using Ajv.

First, you'll need to install the Ajv library using NPM. You can do this by running the following command in your terminal:

npm install ajv

Once you've installed Ajv, you can use it to validate incoming data by creating a middleware function in your Express.js application. Here's an example of what that might look like:

const express = require('express');
const Ajv = require('ajv');
const app = express();

// Define your schema
const schema = {
  type: 'object',
  properties: {
    name: { type: 'string' },
    age: { type: 'number', minimum: 18 },
    email: { type: 'string', format: 'email' }
  },
  required: ['name', 'email']
};

// Create the middleware function
const validateData = (schema) => {
  const ajv = new Ajv();
  return (req, res, next) => {
    const isValid = ajv.validate(schema, req.body);
    if (!isValid) {
      return res.status(400).json(ajv.errors);
    }
    next();
  };
};

// Use the middleware function
app.post('/register', validateData(schema), (req, res) => {
  // Create a new user
  res.status(201).json({ message: 'User created successfully' });
});

In this example, I've created a middleware function called validateData that takes a schema as an argument. The function uses Ajv to validate the incoming data in the req.body object against the schema. If the data is invalid, the middleware function returns a 400 status code with a JSON object containing the validation errors.

I've also used the validateData middleware function in a POST route that creates a new user. If the incoming data is valid, the user is created, and a 201 status code is returned.

Checkout this awesome library 👉 AJV Library