Linear Search

function linearSearch(arr, target) {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] === target) return i;
  }

  return -1;
}

const numbers = [9, 1, 9, 3, -4, 0, 3, 5, 6, 5];
//               0  1  2  3   4  5  6  7  8  9

console.log(linearSearch(numbers, 5)); // 7