I got a Hint from forum, but still have mistake

Tell us what’s happening:

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

Your browser information:

sum([1,2,3,4,5], 10)

Challenge: Replace Loops using Recursion

Link to the challenge:

the array you are testing your function with doesn’t have an element at index 10, so you are trying to sum a number with an undefined value, that will not give you the result you want

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

See this post to find the backtick on your keyboard. The “preformatted text” tool in the editor (</>) will also add backticks around text.

Note: Backticks are not single quotes.