gistfile1.js

(function () {
    // conceal the Thunk class to avoid
    // so that the only way to make one is
    // to call Function::thunk 
    function Thunk(fn, args) {
        this.fn = fn;
        this.args = args;
    }

    Thunk.prototype.force = function () {
        return this.fn.apply(null, this.args);
    };

    Function.prototype.thunk = function () {
        return new Thunk(this, arguments);
    };

    Function.prototype.trampoline = function () {
        var thunk = new Thunk(this, arguments);

        while (thunk instanceof Thunk){
            thunk = thunk.force();
        }

        return thunk;
    };
}());

function even(n){
    return n == 0 ? true
        :  odd.thunk(n - 1);
};

function odd(n){
    return n == 0 ? false
        :  even.thunk(n - 1);
};

console.log(even.trampoline(100001));