demo of how middleware could be implemented with generator

middleware-with-generator.js

class Application {
    constructor() {
        this.middlewares = [];
    }
    use(func) {
        this.middlewares.push(func);
    }
    execute() {
        let stack = [];
        let idx = 0;
        let m = this.middlewares[idx](this.middlewares[++idx]);
        stack.splice(0, 0, m);
        m = m.next();
        while (typeof m.value !== "undefined") {
            m = m.value(this.middlewares[++idx]);
            stack.splice(0, 0, m);
            m = m.next();
        }
        for (let s of stack) {
            s.next();
        }
    }
}

var app = new Application();
var m1 = function*(next) {
    var start = new Date;
    console.log("m1 executing");
    yield next;
    var ms = new Date - start;
    console.log(`m1 executed in ${ms}ms`);
};
app.use(m1);

var m2 = function*(next) {
    var start = new Date;
    console.log("m2 executing");
    yield next;
    var ms = new Date - start;
    console.log(`m2 executed in ${ms}ms`);
};
app.use(m2);

var m3 = function*(next) {
    var start = new Date;
    console.log("m3 executing");
    yield next;
    var ms = new Date - start;
    console.log(`m3 executed in ${ms}ms`);
};
app.use(m3);

var m4 = function*(next) {
    var start = new Date;
    console.log("m4 executing");
    yield next;
    var ms = new Date - start;
    console.log(`m4 executed in ${ms}ms`);
};
app.use(m4);

var m5 = function*(next) {
    var start = new Date;
    console.log("m5 executing");
    yield next;
    var waitTill = new Date(new Date().getTime() + 3 * 1000);
    while (waitTill > new Date()) {}
    var ms = new Date - start;
    console.log(`m5 executed in ${ms}ms`);
};
app.use(m5);

app.execute();
console.log("the end");