Frequently Asked Questions

Does Koa replace Express?

It's more like Connect, but a lot of the Express goodies were moved to the middleware level in Koa to help form a stronger foundation. This makes middleware more enjoyable and less error-prone to write, for the entire stack, not just the end application code.

Typically many middleware would re-implement similar features, or even worse incorrectly implement them, when features like signed cookie secrets among others are typically application-specific, not middleware specific.

Does Koa replace Connect?

No, just a different take on similar functionality now that async functions allow us to write code with fewer callbacks. Connect is equally capable, and some may still prefer it, it's up to what you prefer.

Does Koa include routing?

No - out of the box Koa has no form of routing, however many routing middleware are available:

Why isn't Koa just Express 4.0?

Koa is a pretty large departure from what people know about Express, the design is fundamentally much different, so the migration from Express 3.0 to this Express 4.0 would effectively mean rewriting the entire application, so we thought it would be more appropriate to create a new library.

What custom properties do the Koa objects have?

Koa uses its own custom objects: ctx, ctx.request, and ctx.response. These objects abstract node's req and res objects with convenience methods and getters/setters. Generally, properties added to these objects must obey the following rules:

Many of ctx.request and ctx.response's properties are delegated to ctx. If it's a getter/setter, then both the getter and the setter will strictly correspond to either ctx.request or ctx.response.

Please think about these rules before suggesting additional properties.