Keep optional dependencies in build.

grunt/config/update_json.js

@@ -19,7 +19,8 @@ module.exports = {
             'repository': null,
             'keywords': null,
             'main': null,
-            'dependencies': null
+            'dependencies': null,
+            'optionalDependencies': null
         }
     },
     bower: {

package.json

@@ -34,6 +34,9 @@
     "load-grunt-config": "^0.16.0",
     "lodash": "^4.17.11"
   },
+  "optionalDependencies": {
+    "react-native-crypto": "^2.2.0"
+  },
   "keywords": [
     "security",
     "crypto",

src/core.js

@@ -29,6 +29,13 @@ var CryptoJS = CryptoJS || (function (Math, undefined) {
         } catch (err) {}
     }
 
+    // React native crypto import via require (React Native)
+    if (!crypto && typeof require === 'function') {
+        try {
+            crypto = require('react-native-crypto');
+        } catch (err) {}
+    }
+
     /*
      * Cryptographically secure pseudorandom number generator
      *