// koa 中间件机制 koa1基于迭代器和生成器+prommsie（es6） koa2基于 async/await（es7）
class Koa {
constructor() {
this.middlewares = []
}
use(middleware) {
this.middlewares.push(middleware)
}
compose() {
return async () => {
function createNext(middleware, oldNext) {
return async function() {
await middleware(oldNext)
}
}
let len = this.middlewares.length
let next = async function() {
return Promise.resolve()
}
for (; len--;) {
next = createNext(this.middlewares[len], next)
}
await next()
}
}
}
let koa_app = new Koa()
koa_app.use(async (next) => {
console.log('m1')
await next()
})
koa_app.use(async (next) => {
console.log('m2')
await next()
})
koa_app.use(async (next) => {
console.log('m3')
await next()
})
let fn = koa_app.compose()
fn()
// express中间件机制 基于函数的回调 （es5）
function express() {
var funcs = []
var app = function() {
var i = 0
function next() {
var tesk = funcs[i++]
if (!tesk) {
return
}
tesk(next)
}
next()
}
app.use = function (task) {
funcs.push(task)
}
return app
}
var app = express()
app.use((next) => {
console.log('n1')
next()
})
app.use((next) => {
console.log('n2')
next()
})
app.use((next) => {
console.log('n3')
next()
})
app()