Foo = function(){}
Foo.prototype = {
    around: function(name, pre, post) {
        old = this[name]
        this[name] = function() {
            pre()
            old()
            post()
        }
    },
    met: function(){print("met")}
}

f = new Foo
f.met()
f.around('met', function(){print("pre")}, function(){print("post")})
f.met()