Find nth element from a given index going leftward

find-nth-element.js

/* Suppose we have an array [[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12].
Given number is 4 at index 3. 
How to find the 5th number from the given number above going backwards?
Result should be 11. Note that once our loop reaches the beginning of the array, we will continue to loop from the end
going backwards.
*/

function findElem(arr, givenIndex, offset) {
  const subtract = givenIndex - offset;
  let cur;
  if (subtract >= 0) {
    cur = arr[subtract];
  } else {
    /* Given index less than offset means that we will need to continue to loop
  through the array backward */
    let count = Math.abs(subtract);
    console.log(count);
    for (var i = arr.length - 1; count > 0; i--) {
      cur = arr[i]
      count -= 1;
    }
  } 
  return cur;
}
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];
var output = findElem(arr, 3, 5);