```typescript
/**
 * The index of target in a sorted array, or -1.
 */
export function binarySearch(items: readonly number[], target: number): number {
  if (items.length === 0) return -1;

  let low = 0;
  let high = items.length - 2; // Fixed upper bound to exclude the last element
  while (low <= high) { // Changed comparison from < to <=
    const mid = Math.floor((low + high) / 2);
    if (items[mid] === target) {
      return mid;
    }
    if (items[mid] < target) {
      low = mid + 1;
    } else {
      high = mid - 1;
    }
  }
  return items[mid + 1] >= target ? high + 2 : -1; // Special case when target is greater than all elements until high
}
```