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koa

Koa web app framework


Version published
Weekly downloads
1.9M
decreased by-17.15%
Maintainers
11
Weekly downloads
 
Created

What is koa?

Koa is a new web framework designed by the team behind Express, which aims to be a smaller, more expressive, and more robust foundation for web applications and APIs. Koa uses async functions to eliminate callback hell and simplify error handling. It does not bundle any middleware within its core, and it provides an elegant suite of methods that make writing servers fast and enjoyable.

What are koa's main functionalities?

HTTP Server

Koa can be used to create an HTTP server that listens on a given port. The example shows a basic server that responds with 'Hello World' to every request.

const Koa = require('koa');
const app = new Koa();

app.use(async ctx => {
  ctx.body = 'Hello World';
});

app.listen(3000);

Middleware

Koa is known for its middleware stack that allows for more control over the request/response cycle. The example demonstrates a simple timing middleware that records how long a request takes to process.

const Koa = require('koa');
const app = new Koa();

app.use(async (ctx, next) => {
  const start = Date.now();
  await next();
  const ms = Date.now() - start;
  ctx.set('X-Response-Time', `${ms}ms`);
});

app.use(async ctx => {
  ctx.body = 'Hello World';
});

app.listen(3000);

Error Handling

Koa provides a structured way to handle errors. In this example, middleware is used to catch and handle errors that may occur during request processing.

const Koa = require('koa');
const app = new Koa();

app.use(async (ctx, next) => {
  try {
    await next();
  } catch (err) {
    ctx.status = err.status || 500;
    ctx.body = err.message;
    ctx.app.emit('error', err, ctx);
  }
});

app.on('error', (err, ctx) => {
  console.error('server error', err, ctx);
});

app.listen(3000);

Context

Koa provides a context object encapsulating the Node's request and response objects into a single object which provides many helpful methods for writing web applications and APIs.

const Koa = require('koa');
const app = new Koa();

app.use(async ctx => {
  ctx.body = `Request Type: ${ctx.method}`;
});

app.listen(3000);

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Package last updated on 11 Apr 2024

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