What is Middleware in Express and How It Works

Every Express beginner eventually reaches this moment:

You open some backend project and suddenly see this mysterious thing everywhere:

```js id="a72ks1"

app.use()

Then somebody says:

> “Oh that’s middleware.”

And beginners immediately pretend they understood.

Meanwhile internally:

> “What even is this creature?”

Because middleware sounds complicated.

But the reality is surprisingly simple.

Middleware is basically:

> a checkpoint system between request and response.

That’s it.

In this article, we will understand:

* what middleware actually is * where it sits in Express * how request flow works * execution order * role of `next()` * types of middleware * real-world examples like:

* logging * authentication * validation

And no, we are not diving into Express internals deep enough to summon ancient backend demons.

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# First Understand How Request Flow Works

When a user sends request:

```text id="b81ms2" Browser → Server

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