Koa 提供一个 Context 对象，表示一次对话的上下文（包括 HTTP 请求和 HTTP 回复）。通过加工这个对象，就可以控制返回给用户的内容。
Context.response.body属性就是发送给用户的内容。
koa-compose模块可以将多个中间件合成为一个
例子：
const compose = require('koa-compose');
const logger = (ctx, next) => {
console.log(`${Date.now()} ${ctx.request.method} ${ctx.request.url}`);
next();
}
const main = ctx => {
ctx.response.body = 'Hello World';
};
const middlewares = compose([logger, main]);
app.use(middlewares);
Koa2 路由的前缀
var router = new Router({ prefix: '/users' }); router.get('/', ...); // responds to "/users" router.get('/:id', ...); // responds to "/users/:id"
异步处理写法
app.use(async (ctx, next) => {
await next();
ctx.response.type = 'text/html';
ctx.response.body = '<h1>Hello, koa2!</h1>';
});
Koa框架的路由和Get/Post请求的处理方法。
例子（一个简单的登陆逻辑）
const Koa = require('koa');
const router = require('koa-router')();
const bodyParser = require('koa-bodyparser');
const app = new Koa();
router.get('/', async (ctx, next) => {
ctx.response.body = `<h1>Index</h1>
<form action="/signin" method="post">
<p>Name: <input name="name" value="koa"></p>
<p>Password: <input name="password" type="password"></p>
<p><input type="submit" value="Submit"></p>
</form>`;
});
router.post('/signin', async (ctx, next) => {
console.log('look',ctx.request.body);
var
name = ctx.request.body.name || '',
password = ctx.request.body.password || '';
console.log(`signin with name: ${name}, password: ${password}`);
if (name === 'koa' && password === '12345') {
ctx.response.body = `<h1>Welcome, ${name}!</h1>`;
} else {
ctx.response.body = `<h1>Login failed!</h1>
<p><a href="/">Try again</a></p>`;
}
});
app.use(bodyParser());
app.use(router.routes());
app.listen(3000);
console.log(`app started at port 3000...`);
类似的，put、delete、head请求也可以由router处理。
