gistfile1.js

var Advice = function (type, advice) {
    this.type = type;
    this.advice = advice;
};

Advice.adviseMethod = function (method, advice, combine) {
    if (typeof combine != 'function') { // TODO: don't use typeof
        combine = Advice.Types[combine] || Advice.Types.none;
    }

    advice = advice || function () {};

    return combine(method, advice);
};

Advice.prototype.adviseMethod = function (method) {
    return Advice.adviseMethod(method, this.advice, this.type);
};

Advice.Types = {
    // {{{ Advice.Types
    before: function before (method, advice) {
        return function () {
            advice.apply(this, arguments);
            method.apply(this, arguments);
        };
    },

    after: function after(method, advice) {
        return function () {
            var result = method.apply(this, arguments);
            advice.apply(this, arguments);
            return result;
        };
    },

    around: function around(method, advice) {
        return function () {
            var args = [method].concat(arguments);
            return method.apply(this, arguments);
        };
    },

    instead: function instead(method, advice) {
        return advice;
    },

    none: function (method, advice) {
        return method;
    },

    when: function when(method, advice) {
        return function () {
            return advice.apply(this, arguments) &&
                method.apply(this, arguments);
        };
    },

    unless: function unless(method, advice) {
        return function () {
            return advice.apply(this, arguments) ||
                method.apply(this, arguments);
        };
    }
    // }}}
};

var Advisable = function (method) {
    this.method = method;
    this.stack = [];
};

Advisable.prototype.getAdvisedMethod = function () {
    return this.stack.reduce(function (method, advice) {
        return advice.adviseMethod(method);
    }, this.method);
};

Advisable.prototype.apply = function (ctx, args) {
    return this.getAdvisedMethod().apply(ctx, args);
};

Advisable.prototype.toFunction = function () {
    var advisable = this;

    return function () {
        return advisable.apply(this, arguments);
    };
};