SOURCE

function binary_search(arr, key) {
  var low = 0;
  high = arr.length - 1;
  while (low <= high) {
    var mid = parseInt((high + low) / 2);
    if (key == arr[mid]) {
      return mid;
    } else if (key > arr[mid]) {
      low = mid + 1;
    } else if (key < arr[mid]) {
      high = mid - 1;
    } else {
      return - 1;
    }
  }
};

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 23, 44, 86];
var result = binary_search(arr, 10);
alert(result); // 9 返回目标元素的索引值