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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 generators allow us to write code with less callbacks. Connect is equally capable, and some may still prefer it, it's up to what you prefer.

Do generators decrease performance?

Barely - check out the benchmarks in our readme, the numbers are more than fine, and there's no substitute for proper horizontal scaling.

Does Koa include routing?

No - out of the box Koa has no form of routing, however many routing middleware are available: https://github.com/koajs/koa/wiki

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: this, this.request, and this.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:

  • They must be either very commonly used and/or must do something useful
  • If a property exists as a setter, then it will also exist as a getter, but not vice versa

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

Please think about these rules before suggesting additional properties.