Why Global middleware in NestJS? - Purpose & Use Cases

The Big Idea

What if you could write your security checks once and have them work everywhere automatically?

The Scenario

Imagine you have to check user authentication on every single route in your app by writing the same code again and again.

The Problem

Manually adding checks to each route is tiring, easy to forget, and makes your code messy and hard to maintain.

The Solution

Global middleware runs once for all routes automatically, so you write the logic just once and it applies everywhere.

Before vs After

✗ Before

app.get('/profile', checkAuth, handler);
app.get('/settings', checkAuth, handler);

✓ After

app.use(globalAuthMiddleware);
app.get('/profile', handler);
app.get('/settings', handler);

What It Enables

You can enforce rules like authentication or logging across your whole app easily and consistently.

Real Life Example

Every time a user visits any page, global middleware can check if they are logged in and redirect them if not.

Key Takeaways

Manual checks on every route are repetitive and error-prone.

Global middleware runs once for all routes automatically.

This keeps your code clean and your app secure.