lodash/lang/isNaN.js

define(['./isNumber'], function(isNumber) {

  /**
   * Checks if `value` is `NaN`.
   *
   * **Note:** This method is not the same as native `isNaN` which returns `true`
   * for `undefined` and other non-numeric values. See the [ES5 spec](https://es5.github.io/#x15.1.2.4)
   * for more details.
   *
   * @static
   * @memberOf _
   * @category Lang
   * @param {*} value The value to check.
   * @returns {boolean} Returns `true` if `value` is `NaN`, else `false`.
   * @example
   *
   * _.isNaN(NaN);
   * // => true
   *
   * _.isNaN(new Number(NaN));
   * // => true
   *
   * isNaN(undefined);
   * // => true
   *
   * _.isNaN(undefined);
   * // => false
   */
  function isNaN(value) {
    // An `NaN` primitive is the only value that is not equal to itself.
    // Perform the `toStringTag` check first to avoid errors with some host objects in IE.
    return isNumber(value) && value != +value;
  }

  return isNaN;
});