lodash/internal/indexOfNaN.js

define([], function() {

  /**
   * Gets the index at which the first occurrence of `NaN` is found in `array`.
   * If `fromRight` is provided elements of `array` are iterated from right to left.
   *
   * @private
   * @param {Array} array The array to search.
   * @param {number} [fromIndex] The index to search from.
   * @param {boolean} [fromRight] Specify iterating from right to left.
   * @returns {number} Returns the index of the matched `NaN`, else `-1`.
   */
  function indexOfNaN(array, fromIndex, fromRight) {
    var length = array.length,
        index = fromRight ? (fromIndex || length) : ((fromIndex || 0) - 1);

    while ((fromRight ? index-- : ++index < length)) {
      var other = array[index];
      if (other !== other) {
        return index;
      }
    }
    return -1;
  }

  return indexOfNaN;
});