an implementation of middleware composing

middleware-compose.js

class App {
    constructor() {
        this.middlewares = []
    }
    use(...middlewares) {
        this.middlewares.push(...middlewares)
    }
    next(index = 0) {
        let middleware = this.middlewares[index]
        return middleware ? middleware(() => this.next(index + 1)) : null
    }
    then(resolve) {
        resolve(this.next(0))
    }
}

var app = new App()

app.use(async next => {
    console.log(1)
    await next()
    console.log(2)
})

app.use(async next => {
    console.log(3)
    await next()
    console.log(4)
})

app.use(async next => {
    console.log(5)
    await next()
    console.log(6)
})

app.use(async next => {
    console.log(7)
    await next()
    console.log(8)
})

Promise.resolve(app)