What is the difference between using a recursive function in Python and JS?

Trying to use recursive function in JS, but code isn`t work:

let arr = [6, 5, 3, 1, 1, 1, 1]

function sum(ars, i) {
  if (ars.length == i) {
    return 0
  }
  return ars[i] + sum(ars[1])
}
console.log(sum(arr, 0))

// Output: 6

But the same code works in python:

arr = [2,5,3,1,1,1,1]

def sum(array):
    if array==[]:
        return 0
    return array[0]+sum(array[1:])
    
print (sum(arr))

Can anyone explain what is the difference and what am I doing wrong in the JS code?

>Solution :

sum(ars[1])

ars[1] means "access the element at index 1". It does not get the tail of the array (ie, the sub-array from index 1 to n). Element 1 equals 5, so this is doing sum(5), which then gets messed up because the code expects an array, not a number.

To get the tail of an array you can use the slice method:

let arr = [6, 5, 3, 1, 1, 1, 1]

function sum(ars) {
  if (ars.length == 0) {
    return 0
  }
  return ars[0] + sum(ars.slice(1))
}

console.log(sum(arr))