代碼：

// 通過閉包實現單例
const Middlewave = (function(){
    let instance;
    class Middlewave{
        constructor() {
            this.stack = [];    // 中間件調用棧
            return instance || (instance = this);    //    返回單例
        }
        // 註冊中間件
        use(...funcs) {
            // 將中間件push到stack調用棧中
            funcs.forEach(func => this
 
.stack.push(func));
        }
        // 調用下一個中間件
        next() {
            if (this.stackCopy[0]) {
                // 取出當前中間件
                const curWave = this.stackCopy.shift();
                // 執行當前中間件
                // next綁定this，防止this指向被修改
                curWave(this.req, this.res, this.next.bind(this
 
));
            }
        }
        init(req, res) {
            this.req = req;
            this.res = res;
            // 復制一份中間件調用棧調用棧
            this.stackCopy = this.stack.map(item => item);
            // 執行下一步
            this.next();
        }
    }
    return Middlewave;
})();

測試：

const app = new
 
 Middlewave();

function middlewave_a(req, res, next) {
    req.a = true;
    res.a = true;
    console.log(‘a‘, req, res);
    next();
}

function middlewave_b(req, res, next) {
    req.b = true;
    res.b = true;
    console.log(‘b‘, req, res);
    next();
}

function middlewave_c(req, res, next) {
    req.c = true;
    res.c = true;
    console.log(‘c‘, req, res);
}

function middlewave_d(req, res, next) {
    req.d = true;
    res.d = true;
    console.log(‘d‘, req, res);
    next();
}

app.use(middlewave_a);
app.use(middlewave_b);
app.use(middlewave_c);
app.use(middlewave_d);

app.init({name: ‘a‘}, { name: ‘a‘});
app.init({name: ‘b‘}, { name: ‘b‘});
app.init({name: ‘c‘}, { name: ‘c‘});

結果：

實現一個簡易的express中間件