koa.js 是下一代的node.js框架
npm init -y
npm install koa
const Koa = require('koa')
const app = new Koa()
app.use(ctx => {
ctx.body = 'hello koa2'
})
app.listen(3000)
console.log('[demo] start-quick is starting at port 3000')
node server.js
访问 http:localhost:3000
await返回需要是Promise对象async function的同步写法代替传统的callback嵌套const Koa = require('koa');
const app = new Koa();
// x-response-time
app.use(async function (ctx, next) {
const start = new Date();
await next();
const ms = new Date() - start;
ctx.set('X-Response-Time', `${ms}ms`);
});
// logger
app.use(async function (ctx, next) {
const start = new Date();
await next();
const ms = new Date() - start;
console.log(`${ctx.method} ${ctx.url} - ${ms}`);
});
// response
app.use(ctx => {
ctx.body = 'Hello World';
});
app.listen(3000);
const Koa = require('koa');
const fs = require('fs');
const app = new Koa();
async function route(url) {
let filename = `./views/${url}.html`;
return new Promise(function (resolve, reject) {
fs.readFile(filename, 'utf8', function (err, data) {
if (err) {
reject(err);
} else {
resolve(data);
}
})
});
}
app.use(async ctx => {
let html = await route(ctx.request.url);
ctx.body = html;
});
app.listen(3000);
let Koa = require('koa');
let app = new Koa();
let Router = require('koa-router');
let router = new Router();
router.get('/', ctx => {
ctx.body = 'home';
});
router.get('/user', ctx => {
ctx.body = 'user';
});
router.get('/404', ctx => {
ctx.body = '404';
});
app.use(router.routes(),router.allowedMethods());
app.listen(3000);
在koa中，获取GET请求数据源头是koa中request对象中的query方法或querystring方法，query返回是格式化好的参数对象，querystring返回的是请求字符串
const Koa = require('koa');
const app = new Koa();
app.use(ctx => {
let url = ctx.url;
let query = ctx.query;
let querystring = ctx.querystring;
ctx.body = {
url,
query,
querystring
}
});
app.listen(3000);
对于POST请求的处理，koa2没有封装获取参数的方法，需要通过解析上下文context中的原生node.js请求对象req，将POST表单数据解析成query string（例如：a=1&b=2&c=3），再将query string 解析成JSON格式（例如：{"a":"1", "b":"2", "c":"3"}）
const Koa = require('koa');
let querystring = require('querystring');
const app = new Koa();
async function parseBody(req){
return new Promise(function(resolve,reject){
let buffers = [];
req.on('data',function(data){
buffers.push(data);
});
req.on('end',function(){
let result = Buffer.concat(buffers).toString();
resolve(querystring.parse(result));
});
req.on('err',function(err){
reject(err);
});
});
}
app.use(async ctx => {
if (ctx.request.url == '/' && ctx.request.method == 'GET') {
ctx.body = (
`
<form method="post"><input type="text" name="username"/><input type="submit"/></form>
`
)
} else if (ctx.request.url == '/' && ctx.request.method == 'POST') {
let html = await parseBody(ctx.req);
ctx.body = html;
}else{
ctx.body = '404';
}
});
app.listen(3000);
对于POST请求的处理，koa-bodyparser中间件可以把koa2上下文的formData数据解析到ctx.request.body中
安装koa2版本的koa-bodyparser@3中间件
npm install --save koa-bodyparser@3
const Koa = require('koa');
const path = require('path');
const static = require('koa-static');
const app = new Koa();
app.use(static(
path.resolve('./static')
));
app.use(ctx => {
ctx.body = '404';
});
app.listen(3000);
koa提供了从上下文直接读取、写入cookie的方法
const Koa = require('koa');
const path = require('path');
const app = new Koa();
app.use(ctx => {
let visit = ctx.cookies.get('visit');
if(visit){
visit = parseInt(visit)+1;
}else {
visit = 1;
}
ctx.cookies.set('visit',visit);
ctx.body = `这是你的第${visit}次访问`;
});
app.listen(3000);
const Koa = require('koa');
const app = new Koa();
const session = require('koa-session');
app.keys = ['some secret hurr'];
let options = {
}
app.use(session(options,app));
app.use(ctx=>{
let visit = ctx.session.visit;
if(visit){
visit = visit + 1;
}else{
visit = 1;
}
ctx.session.visit = visit;
ctx.body = `${visit}`;
});
app.listen(3000);
const Koa = require('koa');
const views = require('koa-views');
const path = require('path');
const app = new Koa();
app.use(views(path.join(__dirname, './views'), {extension: 'ejs'}));
app.use(async ctx=>{
let title = 'hello koa2';
await ctx.render('index',{title:title});
});
app.listen(3000);