[add] Platform.select

docs/apis/Platform.md

@@ -10,19 +10,36 @@ specific.
 
 `Platform.OS` will be `web` when running in a Web browser.
 
-**userAgent**: string
-
-On Web, the `Platform` module can be also be used to detect the browser
-`userAgent`.
-
-## Examples
-
 ```js
+import { Platform } from 'react-native';
+
 const styles = StyleSheet.create({
   height: (Platform.OS === 'web') ? 200 : 100,
 });
-
-if (Platform.userAgent.includes('Android')) {
-  console.log('Running on Android!');
-}
+```
+
+## Methods
+
+**select**: any
+
+`Platform.select` takes an object containing `Platform.OS` as keys and returns
+the value for the platform you are currently running on.
+
+```js
+import { Platform } from 'react-native';
+
+const containerStyles = {
+  flex: 1,
+  ...Platform.select({
+    android: {
+      backgroundColor: 'blue'
+    },
+    ios: {
+      backgroundColor: 'red'
+    },
+    web: {
+      backgroundColor: 'green'
+    }
+  })
+});
 ```

src/apis/Platform/index.js

@@ -1,8 +1,6 @@
-import { canUseDOM } from 'fbjs/lib/ExecutionEnvironment'
-
 const Platform = {
   OS: 'web',
-  userAgent: canUseDOM ? window.navigator.userAgent : ''
+  select: (obj: Object) => obj.web
 }
 
 module.exports = Platform