y combinator and the calculation of factorial(5)

y.js

// Y combinator
function y(le) {
    return (function (f) {
        return f(f);
    }(
    function (g) {
        return le(function (x) {
            return g(g)(x);
        });
    })
    );
}


// factorial(5)
(y(function (fac) {
    return function (n) {
        return n <= 2 ? n : n * fac(n - 1);
    };
}))(5);