Binary Search (JavaScript)

binarySearch.js

function binarySearch(array, target) {

  var startIndex = 0,
      stopIndex = array.length - 1,
      middle,
      count = 0;

  while (startIndex < stopIndex) {
    count++;
    middle = ~~((stopIndex + startIndex) / 2);

    // adjust search area
    if (target < array[middle]) {
      stopIndex = middle - 1;
    } else if (target > array[middle]) {
      startIndex = middle + 1;
    } else {
      break; // target is found (or list is exausted)
    }

  }
  // # of iterations
  console.log(count + " iterations");
  
  //make sure it's the right value
  return (array[middle] === target) ? middle : -1;
}

var array = ["a", "b", "c", "d", "e", "f", "h", "i", "j"];
console.log(binarySearch(array, "i")); // 7 found //=> 3 iterations
console.log(binarySearch(array, "b")); // 1 found //=> 2 iterations
console.log(binarySearch(array, "g")); // -1 not found //=> 2 iterations

stopIndex = array.length - 1 not searching last index of array
first index too