Fix #248 by adding a new option deferInitialization

examples/custom-properties/http.js

@@ -32,6 +32,8 @@ const app = new App({
     },
     unhandledRequestTimeoutMillis: 2000, // the default is 3001
   }),
+  // This option enables developer to call #init() in async/await style
+  deferInitialization: true,
 });
 
 app.use(async ({ logger, context, next }) => {
@@ -41,7 +43,12 @@ app.use(async ({ logger, context, next }) => {
 
 (async () => {
   // Start your app
-  await app.start(process.env.PORT || 3000);
-
+  try {
+    await app.init();
+    await app.start(process.env.PORT || 3000);
+  } catch (e) {
+    console.error(e);
+    process.exit(255);
+  }
   console.log('⚡️ Bolt app is running!');
 })();

examples/custom-properties/package.json

@@ -2,10 +2,10 @@
   "name": "bolt-js-custom-properties-app",
   "version": "1.0.0",
   "description": "Having custom request properties in ⚡️ Bolt for JavaScript",
-  "main": "app.js",
+  "main": "http.js",
   "scripts": {
     "ngrok": "ngrok http 3000",
-    "start": "node app.js",
+    "start": "node http.js",
     "test": "echo \"Error: no test specified\" && exit 1"
   },
   "license": "MIT",

src/App.spec.ts

@@ -417,6 +417,49 @@ describe('App', () => {
       // Assert
       assert.instanceOf(app, MockApp);
     });
+
+    it('should fail in await App#init()', async () => {
+      // Arrange
+      const fakeConstructor = sinon.fake();
+      const overrides = mergeOverrides(withNoopAppMetadata(), {
+        '@slack/web-api': {
+          WebClient: class {
+            public constructor() {
+              fakeConstructor(...arguments); // eslint-disable-line prefer-rest-params
+            }
+
+            public auth = {
+              test: () => {
+                throw new Error('Failing for init() test!');
+              },
+            };
+          },
+        },
+      });
+
+      const MockApp = await importApp(overrides);
+      const app = new MockApp({
+        token: 'xoxb-completely-invalid-token',
+        signingSecret: 'invalid-one',
+        deferInitialization: true,
+      });
+      // Assert
+      assert.instanceOf(app, MockApp);
+      try {
+        // call #start() before #init()
+        await app.start();
+        assert.fail('The start() method should fail before init() call');
+      } catch (err: any) {
+        assert.equal(err.message, 'This App instance is not yet initialized. Call `await App#init()` before starting the app.');
+      }
+      try {
+        await app.init();
+        assert.fail('The init() method should fail here');
+      } catch (err: any) {
+        assert.equal(err.message, 'Failing for init() test!');
+      }
+    });
+
     // TODO: tests for ignoreSelf option
     // TODO: tests for logger and logLevel option
     // TODO: tests for providing botId and botUserId options