feat(anonymousid): add a method to retrieve the anonymousId

This adds a `getAnonymousId` method to retrieve the current users anonymousId.

It uses `[SEGAnalytics.sharedAnalytics getAnonymousId]` on iOS and `analytics.getAnalyticsContext().traits().anonymousId()` on Android.

Usage:

```
analytics.getAnonymousId((anonymousId: string) => {
  console.log(`anonymousId: ${anonymousId}`)
})
```

Also adds an example to the seed app (demo https://cloudup.com/c0D76MNLEF9).

.gitignore

@@ -12,3 +12,7 @@ vendor/
 .vscode/
 
 packages/test-app/project
+
+.classpath
+.project
+.settings/

packages/core/android/src/main/java/com/segment/analytics/reactnative/core/RNAnalyticsModule.kt

@@ -128,6 +128,10 @@ class RNAnalyticsModule(context: ReactApplicationContext): ReactContextBaseJavaM
     @ReactMethod
     fun disable() =
         analytics.optOut(true)
+
+    @ReactMethod
+    fun getAnonymousId(callback: Callback) =
+        callback.invoke(analytics.getAnalyticsContext().traits().anonymousId())
 }
 
 private infix fun<T: ValueMap> T.from(source: ReadableMap): T {

packages/core/docs/classes/analytics.client.md

@@ -19,6 +19,7 @@
 * [disable](analytics.client.md#disable)
 * [enable](analytics.client.md#enable)
 * [flush](analytics.client.md#flush)
+* [getAnonymousId](analytics.client.md#getanonymousid)
 * [group](analytics.client.md#group)
 * [identify](analytics.client.md#identify)
 * [middleware](analytics.client.md#middleware)
@@ -134,6 +135,25 @@ This is useful when you want to force all messages queued on the device to be up
 
 **Returns:** `Promise`<`void`>
 
+___
+<a id="getanonymousid"></a>
+
+###  getAnonymousId
+
+▸ **getAnonymousId**(callback: *`function`*): `Promise`<`void`>
+
+*Defined in [analytics.ts:305](https://github.com/segmentio/analytics-react-native/blob/master/packages/core/src/analytics.ts#L305)*
+
+Retrieve the anonymousId.
+
+**Parameters:**
+
+| Name | Type |
+| ------ | ------ |
+| callback | `function` |
+
+**Returns:** `Promise`<`void`>
+
 ___
 <a id="group"></a>
 

packages/core/ios/RNAnalytics/RNAnalytics.m

@@ -137,4 +137,10 @@ +(void)initialize {
     [SEGAnalytics.sharedAnalytics disable];
 }
 
+RCT_EXPORT_METHOD(getAnonymousId:(RCTResponseSenderBlock)callback)
+{
+  NSString *anonymousId = [SEGAnalytics.sharedAnalytics getAnonymousId];
+  callback(@[anonymousId]);
+}
+
 @end

packages/core/src/__mocks__/bridge.ts

@@ -3,6 +3,7 @@ export default {
 	disable: jest.fn(),
 	enable: jest.fn(),
 	flush: jest.fn(),
+	getAnonymousId: jest.fn(),
 	group: jest.fn(),
 	identify: jest.fn(),
 	reset: jest.fn(),

packages/core/src/__tests__/analytics.spec.ts

@@ -79,6 +79,8 @@ it('does .flush()', testCall('flush'))
 it('does .enable()', testCall('enable'))
 it('does .disable()', testCall('disable'))
 
+it('does .getAnonymousId()', () => testCall('getAnonymousId')(jest.fn()))
+
 it('logs uncaught bridge errors', async () => {
 	const error = {
 		message: 'test-error'

packages/core/src/analytics.ts

@@ -301,6 +301,11 @@ export module Analytics {
 			await this.wrapper.run('disable', disable => disable())
 		}
 
+		/** Retrieve the anonymousId. */
+		public async getAnonymousId(callback: (anonymousId: string) => void) {
+			await this.wrapper.run('getAnonymousId', getAnonymousId => getAnonymousId(callback))
+		}
+
 		private handleError(error: Error) {
 			const { handlers } = this
 

packages/core/src/bridge.ts

@@ -37,6 +37,7 @@ export interface Bridge {
 	flush(): Promise<void>
 	enable(): Promise<void>
 	disable(): Promise<void>
+	getAnonymousId(callback: (anonymousId: string) => void): Promise<void>
 }
 
 const bridge: Bridge = NativeModules.RNAnalytics

packages/test-app/seed/App.tsx

@@ -33,6 +33,12 @@ const trackOrder = () => {
   })
 }
 
+const logAnonymousId = () => {
+  analytics.getAnonymousId((anonymousId: string) => {
+    console.log(`anonymousId: ${anonymousId}`)
+  })
+}
+
 const buildId = 'CIRCLE_WORKFLOW_ID'
 
 const testSuite = () =>
@@ -61,6 +67,7 @@ export default class App extends Component {
         <Button title="Flush" onPress={flush} />
         <Button title="Track: Pizza Eaten" onPress={pizzaEaten} />
         <Button title="Launch test suite" onPress={testSuite} />
+        <Button title="Log anonymousId" onPress={logAnonymousId} />
       </View>
     )
   }