function indexOfNaN(array, fromIndex, fromRight) {
  var length = array.length,
      index = fromIndex + (fromRight ? 0 : -1);

  while ((fromRight ? index-- : ++index < length)) {
    var other = array[index];
    if (other !== other) {
      return index;
    }
  }
  return -1;
}
Gets the index at which the first occurrence of `NaN` is found in `array`.

@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`.