The code in question is a function to calculate the factorial of an integer value. To calculate the factorial of an integer value, you first check to see if the value is zero. If the value is zero, then the function returns 1. If the value is not zero, the function calculates the factorial of the value - 1 multiplied by the value.
function factorial(n) {
if (n == 0) {
return 1;
} else {
return factorial(n - 1) * n;
}
}