Searching Algorithms (linear search, binary search)

What optimization technique is demonstrated in this linear search variation?
function searchWithSentinel(arr, target) {
  const lastElement = arr[arr.length - 1];
  arr[arr.length - 1] = target;
  
  let i = 0;
  while(arr[i] !== target) i++;
  
  arr[arr.length - 1] = lastElement;
  if(i < arr.length - 1 || lastElement === target) return i;
  return -1;
}
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