underscore.js之sortedIndex

_.sortedIndex = function(array, obj, iteratee, context) {
    iteratee = cb(iteratee, context, 1);
    var value = iteratee(obj);
    var low = 0, high = getLength(array);
    while (low < high) {
      var mid = Math.floor((low + high) / 2);
      if (iteratee(array[mid]) < value) low = mid + 1; else high = mid;
    }
    return low;
  };

  var sortArr = [1, 2, 5, 10, 12]
  查找元素是 8
  var low = 0 初始值
  let high = sortArr.length
  while(low < high) 循环执行直到条件不满足
  while内进行一分为二, 
  向下取整获取中间值, let mid = Math.floor((low + high) / 2) mid = 2
  sortArr(mid) => 5
  条件判断(sortArr(mid) < 进行查找的元素 => 8) 
  执行三遍
  第一遍 5 < 8 low = 3
  第二遍 12 < 8 high = 4
  第三遍 10 < 8 high = 3
  最后 返回 所在位置