A simplified example of Middleware execution.

Middleware.js

/** This is a common question im running into, what is the difference between a promise design pattern and a middleware.. **/
/* This pattern is commonly found in connect, koa, express and other middleware based frameworks. */
/* This is not a hook pattern with pre/post */

function Middleware() {
    if (!(this instanceof Middleware)) {
        if (global.MODE_LVL < 5) {
            console.log('Not an instance; returning new callbackStack Client');
        }
        return new Middleware();
    }
    var _self = this;
    _self.middlewares = new Array();
}

Middleware.prototype.use = function(func) {
    /* Adds to execution stack, return promise of next() */
    var _self = this;
    _self.middlewares.push(func);
    return _self;
};
Middleware.prototype.exec = function() {
    /* Runs the middleware stack and handles the callbacks in subsequent order. */
    var index = 0;
    var stack = this.middlewares;
    function next(err) {
        if(err) {
            console.log(err);
        }
        var s = stack[index++];
        if(!s) {
            return;
        }
        /* Starts the after evaluation iteration */
        call(s, next);
    }
    function call(s, next) {
        /* Executes the callback */
        try {
            s(next);
        } catch (e) {
            error = e;
        }
        next(error);
    }
    next();
};


/* Example of useage */

var c = new Middleware();
c.use(function(next) {
    console.log('1');
    next();
}).use(function(next) {
    console.log('2');
    next();
}).exec();