Learning the Importance of Route Order in Express.js

Introduction

Express.js is one of the most popular frameworks for building Node.js applications. Recently, I faced a bug where an API route kept returning 404 Not Found, even though the controller logic was correct. The issue turned out to be something simple but crucial: route order.

The Problem

I had defined my routes like this:

// Dynamic route to get resource by ID
router.get("/:id", getResourceById);
// Static route to get resource details
router.get("/details", getResourceDetails);

When I tried hitting /details, Express didn’t use getResourceDetails. Instead, it treated "details" as the :id parameter. Since there was no record with that ID, it returned a 404.

Why Does This Happen?

Express matches routes in the order they are defined. The first route that matches the request path is executed. In this case, /:id matched before /details, so the wrong controller was being called.

The Fix

The solution was simple: define the specific route first, and the dynamic route after:

// Static route first
router.get("/details", getResourceDetails);
// Dynamic route after
router.get("/:id", getResourceById);

Now, Express correctly matches /details to the right controller.

Lesson Learned

• Always define static or specific routes before dynamic routes like /:id.
• Route order matters a lot in Express.js.
• A small misplacement can cause hard-to-trace bugs such as unexpected 404s.

Conclusion

This was a simple yet powerful reminder: Express routing is order-dependent. By being mindful of route definitions, we can prevent confusing errors and make our APIs more reliable.

I hope this saves someone else from the hours of debugging I went through!