fix: allow inbox change handlers to be unsubscribed

Author: gyoshev

dist/leanplum.d.ts

@@ -116,7 +116,7 @@ export interface Inbox {
   markAsRead(messageId: string): void;
   read(messageId: string): void;
   remove(messageId: string): void;
-  onChanged(handler: Function): void;
+  onChanged(handler: Function): Function;
   count(): number;
   unreadCount(): number;
   allMessages(): InboxMessage[];

src/LeanplumInbox.ts

@@ -76,8 +76,9 @@ export default class LeanplumInbox implements Inbox {
     this.createRequest('deleteNewsfeedMessage', args, {})
   }
 
-  public onChanged(handler: Function): void {
-    this.changeHandlers.push(handler)
+  public onChanged(handler: Function): Function {
+    const idx = this.changeHandlers.push(handler)
+    return () => this.changeHandlers.splice(idx-1, 1)
   }
 
   private triggerChangeHandlers(): void {

test/specs/LeanplumInbox.test.ts

@@ -73,6 +73,19 @@ describe(LeanplumInbox, () => {
       expect(handler).toHaveBeenCalledTimes(0)
       expect(inbox.messageIds()).toEqual([])
     })
+
+    it('allows change handlers to be unsubscribed', () => {
+      const handler = jest.fn()
+
+      const remove = inbox.onChanged(handler)
+      remove();
+
+      mockMessages({
+        '123##1': {},
+      })
+
+      expect(handler).toHaveBeenCalledTimes(0)
+    })
   })
 
   describe('allMessages', () => {