Middleware explained simply

What Is Middleware? (Straightforward Explanation)

Middleware is code that runs between a request and a response. It’s the logic that sits in the middle deciding what happens before your app sends a final reply.

⸻

Why It Exists

Every system that handles requests needs to do things like: • Log data • Check authentication • Validate inputs • Handle errors

Instead of mixing all that inside every route or function, we use middleware small, focused pieces that process the request step by step.

⸻

How It Works

When a request comes in, it passes through a chain of middleware. Each one can: • Inspect or modify the request • Stop the process and send a response • Or pass the request to the next middleware

If one stops the flow (for example, returns “Unauthorized”), the rest never run.

⸻

The Flow

Request ↓ [Middleware 1] → logs request ↓ [Middleware 2] → checks authentication ↓ [Middleware 3] → validates input ↓ [Handler] → main logic ↓ Response

⸻

Why It’s Useful • Keeps your code clean and organized • Makes logic reusable • Simplifies maintenance and testing

⸻

Universal Example (Pseudo Code)

middlewares = [log, auth, validate]

function handleRequest(req): for m in middlewares: result = m(req) if result == "STOP": return "Response sent" return "Main response"

No matter what language you use JavaScript, Python, Java, Go this pattern stays the same.

⸻

TL;DR

Middleware is the “in-between” code that processes requests before they reach your core logic. It filters, checks, or modifies making your app modular, safe, and clean.