Bump to v4.0.0.

isUndefined.js

@@ -0,0 +1,27 @@
+define([], function() {
+
+  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
+  var undefined;
+
+  /**
+   * Checks if `value` is `undefined`.
+   *
+   * @static
+   * @memberOf _
+   * @category Lang
+   * @param {*} value The value to check.
+   * @returns {boolean} Returns `true` if `value` is `undefined`, else `false`.
+   * @example
+   *
+   * _.isUndefined(void 0);
+   * // => true
+   *
+   * _.isUndefined(null);
+   * // => false
+   */
+  function isUndefined(value) {
+    return value === undefined;
+  }
+
+  return isUndefined;
+});