koa
Koa中最重要的概念：middleware, context, request, response
const Koa = require('koa');
const app = new Koa();
// koa 中间件的写法与执行顺序
app.use(async (ctx, next) => {
// 1
await next(); // 2
console.log(`${ctx.method} ${ctx.url} ${ctx.response.get('X-Res-Time')}`); // 8
});
app.use(async (ctx, next) => {
const start = Date.now(); // 3
await next(); //4
const ms = Date.now() - start; // 6
ctx.response.set('X-Res-Time', `${ms}ms`); // 7
});
app.use(async ctx => {
ctx.body = 'hello koajs'; // 5
});
app.listen(3000); // http.createServer(app.callback()).listen(3000);
1.1 Context
Context对象在每次请求的时候创建，它主要是对nodejs的request和response的封装
app.use(async ctx => {
ctx; // is the Context
ctx.request; // is a Koa Request
ctx.response; // is a Koa Response
ctx.app; // is a Koa Application
ctx.state.user = await User.find(id);
// ctx.state is the recommended namespace for passing information through middleware
ctx.cookie; // cookie object
});
1.2 Request
app.use(async ctx => {
ctx.request; // is a Koa Request
ctx.request.header; // request header
ctx.request.method; // request method
ctx.request.url; // request url
ctx.request.query; // convert 'color=blue&size=s' to {color:'blue', size: 's'}
ctx.request.get(field); // get specific field in header
});
1.3 Response
app.use(async ctx => {
ctx.response; // is a Koa Request
ctx.response.status = 200;
ctx.response.body = 'hello world';
ctx.response.type = 'text/plain; charset=utf-8';
ctx.set({
'Etag': '1234',
'Last-Modified': date
});
ctx.set('Cache-Control', 'no-cache');
const etag = ctx.response.get('ETag'); // case-insensitive
});