gistfile1.js

function Thunk(f) {
    this.f = f;
}

function trampoline(f) {
    return function() {
        var result = f.apply(this, arguments);
        while (result instanceof Thunk) {
            result = result.f();
        }
        return result;
    };
}

function factorial(n) {
    var _factorial = trampoline(function self(acc, n) {
        if (n > 0) {
            return new Thunk(function() { return self(acc * n, n - 1); });
        } else {
            return acc;
        }
    });
  
    return _factorial(1, n);
}