Koa.js
Next-generation Node.js framework for building web apps and APIs
About Koa.js
Koa.js is a lightweight, expressive web framework created by the Express team. Designed for modern Node.js applications, it leverages async functions to eliminate callbacks and simplify error handling. With a minimal core and powerful middleware system, Koa provides an elegant foundation for developing robust web applications and APIs.
FAQ
Koa requires Node.js version 18.0.0 or higher to support ES2015 and async functions.
You can install Koa using npm with the command `npm i koa`. Ensure you have Node.js v18.0.0 or higher installed first.
Yes, Koa is designed to be interoperable with other middleware systems like Express or Connect. You can mount a Koa app within an Express or Connect app using `app.callback()`.
Koa middleware is executed in a stack-like manner using async functions. When `next()` is called, the function suspends and passes control to the next middleware. After the downstream middleware completes, control flows back upstream, allowing each middleware to perform its post-processing.
Koa supports several application settings such as `app.env` (defaults to NODE_ENV or 'development'), `app.proxy` (trust proxy headers), `app.subdomainOffset`, `app.proxyIpHeader`, `app.maxIpsCount`, and `app.asyncLocalStorage` for enabling async local storage.
Koa emits an 'error' event for logging purposes. You can add a custom error handler using `app.on('error', err => { ... })`. By default, errors are output to stderr unless `app.silent` is true. Errors with `err.status` of 404 or `err.expose` set to true are not logged.
You can set signed cookies by configuring `app.keys` with an array of keys or a KeyGrip instance. Then, use `ctx.cookies.set('name', 'value', { signed: true })` to set a signed cookie.
`app.context` is the prototype for the `ctx` object created for each request. You can add custom properties or methods to `app.context` to make them available across your entire application, which can improve performance by avoiding middleware.
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