Y-Combinator in JS for factorization

y-combinator.js

var Y = function (F) {
    return (function (x) {
        return F(function (y) {
            return (x(x))(y);
        });
    })(function (x) {
        return F(function (y) { 
            return (x(x))(y);
        });
    });
};

var FactGen = function (fact) {
    return (function(n) {
        return ((n === 0) ? 1 : (n*fact(n-1)));
    });
};

console.log((Y(FactGen))(3));