hi!

Can someone help me with this code please? I don’t undestand how it works:

Write a recursive function, `sum(arr, n)`

, that returns the sum of the first `n`

elements of an array `arr`

.

```
function sum(arr, n) {
if(n <= 0) {
return 0;
} else {
return sum(arr, n - 1) + arr[n - 1];
}
}
```

I know this is the answer, but I can notunderstand the way of testing it.

`sum([2, 3, 4, 5], 3)`

should equal 9.

`sum([2, 3, 4], 1)`

should equal 2.

`sum([1], 0)`

should equal 0.

Thank you in advance!