Question

How do you implement API request validation in Express using middleware?

How can I implement API request validation in Express using middleware? I want to ensure that incoming requests have the required data and follow the correct format before reaching my route handlers. What’s the best approach for setting up validation as middleware? Are there any libraries, like Joi or express-validator, that would simplify this process?

Answer 1

1. Create Middleware Function : 
- Define a custom middleware function that takes req, res , and next as parameters. Use validation libraries like joi , express-validator, or custom validation logic.

2. Validate Request Data :
- Extract the relevant data from the request body , query parameters , or headers. Apply validation rules using the chosen library or custom logic.

3. Error Handling :
- Implement a global error handler middleware to catch validation errors and other errors. Send a formatted error response to the client , including a suitable HTTP status code and error details.

//javascript

const express = require('express');

const Joi = require('joi');

const app = express();

const userSchema = Joi.object({

name: Joi.string().required(),

email: Joi.string().email().required(),

age: Joi.number().min(18).max(100),

});

function validateUser(req , res , next ){

const {error} = userSchema.validate(req.body);

if(error) {

return next(error);

}

next();

}

app.post('/users' , validateUser , (req , res) => {

// Create a new user

});

app.use((err , req , res , next ) => {

res.status(400).json({error: err.message });

});