Add isFullUser helper function

index.ts

@@ -17,3 +17,9 @@ export { UserDescriptionEntity } from './types/user_description_entity';
 export { UserEntities } from './types/user_entities';
 export { UserMentionEntity } from './types/user_mention_entity';
 export { UserUrlEntity } from './types/user_url_entity';
+
+import { FullUser, User } from './types/user';
+
+export function isFullUser(user: User): user is FullUser {
+  return 'screen_name' in user;
+}

readme.md

@@ -15,7 +15,7 @@ _Note that the presence of field is not an indication of it being current and ac
 Install
 ----
 
-```
+```bash
 npm install --save-dev twitter-d
 ```
 
@@ -24,7 +24,7 @@ Usage
 
 The main two interfaces provided are [`Status`](https://github.com/abraham/twitter-d/blob/master/types/status.d.ts) and [`User`](https://github.com/abraham/twitter-d/blob/master/types/user.d.ts) although there are a number of related interfaces like [`MediaEntity`](https://github.com/abraham/twitter-d/blob/master/types/media_entity.d.ts) and [`AdditionalMediaInfo`](https://github.com/abraham/twitter-d/blob/master/types/additional_media_info.d.ts).
 
-```
+```typescript
 import { Status as Tweet, User } from 'twitter-d';
 
 function getTweet(): Tweet { /* ... */ }
@@ -33,10 +33,27 @@ function getUser(): User { /* ... */ }
 
 Or if you are using [TypeScript 2.9+](https://blogs.msdn.microsoft.com/typescript/2018/05/31/announcing-typescript-2-9/#import-types) you can use `import()`.
 
-```
+```typescript
 function getStatus(): import('twitter-d').Status { /* ... */ }
 ```
 
+User
+----
+
+In some contexts, using `trim_user=true` on [GET statuses/mentions_timeline](https://developer.twitter.com/en/docs/tweets/timelines/api-reference/get-statuses-mentions_timeline), you might get a user object that only includes `id` and `id_str`. To test if a `User` value is a `FullUser` you can use the `isFullUser` helper function.
+
+```typescript
+import { isFullUser, User } from 'twitter-d';
+
+function logUser(user: User) {
+  if (isFullUser(user)) {
+    console.log(user.name);
+  } else {
+    throw new Error('User is not type FullUser');
+  }
+}
+```
+
 Contributing
 ----