what is a difference

Question

what is a difference between 1 and 2:

1. function one(){
let ball = 10
}

2.function one(){
ball = 10
}

and which situations we can use any of them (if there is a difference)

Answer 1

use 1 when you only want to use the variable in the function because it will not work anywhere else but use 2 when reassigning a globally scoped variable one which is not in a function then just gets reassigned in a function this variable is visible everywhere that is why it is called global scoping.

Answer 2

Don't use 2 function at all.