lodash/internal/indexOfNaN.js

/**
 * 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;
}

module.exports = indexOfNaN;