What is Middleware in Express and How It Works

Middleware in Express.js are the function that Run during the request response cycle to process the input and Modify the response and control the application flow. As many time in basic App.js we write app.use(express.json()) this is also a middleware .

Basic syntax of middleware is

(req,res,next)=>{
    //body of middleware
}

Next in the middleware is like the boundary for the middleware to go on upcoming middleware .

Let's understand uses of the middleware according to their importance.

• Security (CORS ), Authentication and Rate Limiting Middleware.

• Logging and monitoring middleware .

• Global error handling Middleware .

• Compression .

• Data Parsing middleware.

Types of middleware

1 :- Application level

Application level middleware are registered using app.use() and they are executed for all the router and HTTP , commonly used for logging ,authentication, body parsing etc .

2:- Router Level

Router level middleware are registered using router.use() and executed for only the router level and commonly used for the code organizing and maintianblity .

3:- Error handling middleware

Error handling middleware is commonly used for capturing and processing runtime errors during the req-res cycle .

4:- Build-in middleware

Express offers built-in middleware functions to handle common server tasks efficiently.

• express.static() serves static files like images, CSS, and JS.

• express.json() parses incoming JSON request bodies.

Middleware chaining :-

Using middleware constistently one after one is known as middleware chaining .