Bump to v4.0.0.

isNaN.js

@@ -0,0 +1,35 @@
+define(['./isNumber'], function(isNumber) {
+
+  /**
+   * Checks if `value` is `NaN`.
+   *
+   * **Note:** This method is not the same as [`isNaN`](https://es5.github.io/#x15.1.2.4)
+   * which returns `true` for `undefined` and other non-numeric values.
+   *
+   * @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 ActiveX objects in IE.
+    return isNumber(value) && value != +value;
+  }
+
+  return isNaN;
+});