93 lines
3.5 KiB
Markdown
93 lines
3.5 KiB
Markdown
# Koa vs Express
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Philosophically, Koa aims to "fix and replace node", whereas Express "augments node".
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Koa uses promises and async functions to rid apps of callback hell and simplify error handling.
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It exposes its own `ctx.request` and `ctx.response` objects instead of node's `req` and `res` objects.
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Express, on the other hand, augments node's `req` and `res` objects with additional properties and methods
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and includes many other "framework" features, such as routing and templating, which Koa does not.
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Thus, Koa can be viewed as an abstraction of node.js's `http` modules, where as Express is an application framework for node.js.
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| Feature | Koa | Express | Connect |
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|------------------:|-----|---------|---------|
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| Middleware Kernel | ✓ | ✓ | ✓ |
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| Routing | | ✓ | |
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| Templating | | ✓ | |
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| Sending Files | | ✓ | |
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| JSONP | | ✓ | |
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Thus, if you'd like to be closer to node.js and traditional node.js-style coding, you probably want to stick to Connect/Express or similar frameworks.
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If you want to get rid of callbacks, use Koa.
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As result of this different philosophy is that traditional node.js "middleware", i.e. functions of the form `(req, res, next)`, are incompatible with Koa. Your application will essentially have to be rewritten from the ground, up.
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## Does Koa replace Express?
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It's more like Connect, but a lot of the Express goodies
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were moved to the middleware level in Koa to help form
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a stronger foundation. This makes middleware more enjoyable
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and less error-prone to write, for the entire stack, not
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just the end application code.
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Typically many middleware would
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re-implement similar features, or even worse incorrectly implement them,
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when features like signed cookie secrets among others are typically application-specific,
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not middleware specific.
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## Does Koa replace Connect?
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No, just a different take on similar functionality
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now that generators allow us to write code with less
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callbacks. Connect is equally capable, and some may still prefer it,
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it's up to what you prefer.
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## Why isn't Koa just Express 4.0?
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Koa is a pretty large departure from what people know about Express,
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the design is fundamentally much different, so the migration from
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Express 3.0 to this Express 4.0 would effectively mean rewriting
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the entire application, so we thought it would be more appropriate
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to create a new library.
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## How is Koa different than Connect/Express?
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### Promises-based control flow
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No callback hell.
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Better error handling through try/catch.
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No need for domains.
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### Koa is barebones
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Unlike both Connect and Express, Koa does not include any middleware.
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Unlike Express, routing is not provided.
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Unlike Express, many convenience utilities are not provided. For example, sending files.
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Koa is more modular.
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### Koa relies less on middleware
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For example, instead of a "body parsing" middleware, you would instead use a body parsing function.
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### Koa abstracts node's request/response
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Less hackery.
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Better user experience.
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Proper stream handling.
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### Koa routing (third party libraries support)
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Since Express comes with its own routing, but Koa does not have
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any in-built routing, there are third party libraries available such as
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koa-router and koa-route.
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Similarly, just like we have helmet for security in Express, for Koa
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we have koa-helmet available and the list goes on for Koa available third
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party libraries.
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