binarySearch.js

/**
 * @param {Array<number>} arr Numeric array
 * @param {number} needle Value to search for
 * @return {number} -1 if value was not found, positive value index otherwise
 */
function binarySearch(arr, needle) {
  if (!Array.isArray(arr) || needle == null) {
    return -1;
  }

  // pre-requisite: sort the array, ascending order
  arr.sort();

  let leftPtr = 0,
    rightPtr = arr.length - 1,
    midPtr;
  
  while (leftPtr <= rightPtr) {
    midPtr = Math.floor((leftPtr + rightPtr) / 2);
    if (arr[midPtr] === needle) {
      return midPtr;
    } else if (arr[midPtr] < needle) {
      // value at the middle pointer is smaller than the needle,
      // that means we need to shift to the right side,
      // by moving the left pointer to middle pointer + 1
      leftPtr = midPtr + 1;
    } else {
      // value at the middle pointer is bigger than the target,
      // that means we need to shift to the left side,
      // by moving the right pointer to middle pointer - 1
      rightPtr = midPtr - 1;
    }
  }

  return -1;
}