Compile example project (line#736)

I found example project cannot be compiled by tsc, so this change fixes
it and adds a build script to check there is no error in CI.

Author: Yang-33

.github/workflows/test.yml

@@ -44,3 +44,10 @@ jobs:
       run: export NODE_OPTIONS=--max-old-space-size=6144; npm test
     - name: Test building docs
       run: export NODE_OPTIONS=--openssl-legacy-provider; npm run docs:build
+    - name: Test building examples
+      run: |
+        cd examples/echo-bot-ts
+        npm run build-sdk
+        npm install
+        npm run build
+        cd -

examples/echo-bot-ts/index.ts

@@ -28,10 +28,14 @@ const client = new messagingApi.MessagingApiClient(clientConfig);
 // Create a new Express application.
 const app: Application = express();
 
+const isTextEvent = (event: any): event is webhook.MessageEvent & { message: webhook.TextMessageContent } => {
+  return event.type === 'message' && event.message && event.message.type === 'text';
+};
+
 // Function handler to receive the text.
 const textEventHandler = async (event: webhook.Event): Promise<MessageAPIResponseBase | undefined> => {
   // Process all variables here.
-  if (event.type !== 'message' || !event.message || event.message.type !== 'text') {
+  if (!isTextEvent(event)) {
     return;
   }