crazy JS factorial :)

fact.js

var N = 10;
(function(N){
    var arr = [];
    for(var i=N+1; i--;) arr.push(i);
    arr.pop(); // last elem is 0
    return arr;
})(N).reduce(function (n, i) {
    return n * i;
}, 1);

function fact(n, cb) {
    if (n < 1) return cb(null, 1);
    setImmediate(fact.bind(this, n-1, function(err, nn) {
        cb(null, n * nn);
    }));
}

👍