为什么阶乘 function 返回的不是 1？

Question

I can't understand why the function returned a result and not a unit, how does it work?

function factorial(n) {
  return (n != 1) ? n * factorial(n - 1) : 1;
}

console.log(factorial(5)); // result is 120 why not 1 ?

Answer 1

This is a recursive function. You start by passing in 5 . It then calls itself with 4 , and so on. The math for each call looks like this:

factorial(5): 5 * factorial(4)
factorial(4): 4 * factorial(3)
factorial(3): 3 * factorial(2)
factorial(2): 2 * factorial(1)
factorial(1): 1

Once you get to the "base case", 1, execution goes back up the stack in reverse order and uses the result of each previous step:

factorial(1): 1
factorial(2): 2 * 1 = 2
factorial(3): 3 * 2 = 6
factorial(4): 4 * 6 = 24
factorial(5): 5 * 24 = 120

And so factorial(5) returns 120.