function sortedIndex(array, value, callback, thisArg) {
      var low = 0,
          high = array ? array.length : low;

      // explicitly reference `identity` for better inlining in Firefox
      callback = callback ? lodash.createCallback(callback, thisArg, 1) : identity;
      value = callback(value);

      while (low < high) {
        var mid = (low + high) >>> 1;
        (callback(array[mid]) < value)
          ? low = mid + 1
          : high = mid;
      }
      return low;
    }
Uses a binary search to determine the smallest index at which a value
should be inserted into a given sorted array in order to maintain the sort
order of the array. If a callback is provided it will be executed for
`value` and each element of `array` to compute their sort ranking. The
callback is bound to `thisArg` and invoked with one argument; (value).

If a property name is provided for `callback` the created "_.pluck" style
callback will return the property value of the given element.

If an object is provided for `callback` the created "_.where" style callback
will return `true` for elements that have the properties of the given object,
else `false`.

@static
@memberOf _
@category Arrays
@param {Array} array The array to inspect.
@param {*} value The value to evaluate.
@param {Function|Object|string} [callback=identity] The function called
 per iteration. If a property name or object is provided it will be used
 to create a "_.pluck" or "_.where" style callback, respectively.
@param {*} [thisArg] The `this` binding of `callback`.
@returns {number} Returns the index at which `value` should be inserted
 into `array`.
@example

_.sortedIndex([20, 30, 50], 40);
// => 2

// using "_.pluck" callback shorthand
_.sortedIndex([{ 'x': 20 }, { 'x': 30 }, { 'x': 50 }], { 'x': 40 }, 'x');
// => 2

var dict = {
  'wordToNumber': { 'twenty': 20, 'thirty': 30, 'fourty': 40, 'fifty': 50 }
};

_.sortedIndex(['twenty', 'thirty', 'fifty'], 'fourty', function(word) {
  return dict.wordToNumber[word];
});
// => 2

_.sortedIndex(['twenty', 'thirty', 'fifty'], 'fourty', function(word) {
  return this.wordToNumber[word];
}, dict);
// => 2