Bump to v4.0.0.

isFunction.js

@@ -0,0 +1,40 @@
+import isObject from './isObject';
+
+/** `Object#toString` result references. */
+var funcTag = '[object Function]',
+    genTag = '[object GeneratorFunction]';
+
+/** Used for built-in method references. */
+var objectProto = Object.prototype;
+
+/**
+ * Used to resolve the [`toStringTag`](http://ecma-international.org/ecma-262/6.0/#sec-object.prototype.tostring)
+ * of values.
+ */
+var objectToString = objectProto.toString;
+
+/**
+ * Checks if `value` is classified as a `Function` object.
+ *
+ * @static
+ * @memberOf _
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is correctly classified, else `false`.
+ * @example
+ *
+ * _.isFunction(_);
+ * // => true
+ *
+ * _.isFunction(/abc/);
+ * // => false
+ */
+function isFunction(value) {
+  // The use of `Object#toString` avoids issues with the `typeof` operator
+  // in Safari 8 which returns 'object' for typed array constructors, and
+  // PhantomJS 1.9 which returns 'function' for `NodeList` instances.
+  var tag = isObject(value) ? objectToString.call(value) : '';
+  return tag == funcTag || tag == genTag;
+}
+
+export default isFunction;