Add flow head-line. Add is.js

Author: nodkz

src/index.js

@@ -1,3 +1,5 @@
+/* @flow */
+
 import { mongooseModelToTypeComposer } from './modelConverter';
 
 export default mongooseModelToTypeComposer;

src/utils/index.js

@@ -1,13 +1,12 @@
+/* @flow */
 import toDottedObject from './toDottedObject';
+import { isObject } from './is';
 
 export {
   toDottedObject,
+  isObject,
 };
 
 export function upperFirst(string: string): string {
   return string.charAt(0).toUpperCase() + string.slice(1);
 }
-
-export function isObject(value: mixed): boolean {
-  return typeof value === 'object' && !Array.isArray(value) && value !== null;
-}

src/utils/is.js

@@ -0,0 +1,13 @@
+/* @flow */
+
+export function isString(value: mixed): boolean {
+  return typeof value === 'string';
+}
+
+export function isObject(value: mixed): boolean {
+  return typeof value === 'object' && !Array.isArray(value) && value !== null;
+}
+
+export function isFunction(value: mixed): boolean {
+  return !!(value && value.constructor && value.call && typeof value === 'function' && value.apply);
+}