Calculate the factorial of a number passed as the single parameter of a function

factorial.js

function fact() {
  arr = [];
  var n = arguments[0];
  if (n == 0) {
    arr.push(1);
  } else {
    for (i = 1; i <= n; i++) {
      arr.push(i);
    }
  }
  var result = arr.reduce(function(a, b) {
    return a * b;
  });
  console.log(result);
}
fact(1);