JavaScript: clone a function

What is a fastest way to clone a function in JavaScript (with or without its properties)?

Two options coming to mind are eval(func.toString()) and function() { return func.apply(..) }. But I am worried about performance of eval and wrapping will make stack worse and will probably degrade performance if applied a lot or applied to already wrapped.

new Function(args, body) looks nice, but how exactly can I reliable split existing function to args and body without a JS parser in JS?

Update: What I mean is being able to do

var funcB = funcA.clone(); // where clone() is my extension
funcB.newField = {...};    // without affecting funcA

try this:

var x = function() {
    return 1;
};

var t = function(a,b,c) {
    return a+b+c;
};


Function.prototype.clone = function() {
    var that = this;
    var temp = function temporary() { return that.apply(this, arguments); };
    for(var key in this) {
        if (this.hasOwnProperty(key)) {
            temp[key] = this[key];
        }
    }
    return temp;
};

alert(x === x.clone());
alert(x() === x.clone()());

alert(t === t.clone());
alert(t(1,1,1) === t.clone()(1,1,1));
alert(t.clone()(1,1,1));