Fix custom broadcaster usages (#404)

* Fix custom broadcaster usages

* improve test

* lint

* styleci

Author: bytestream

src/echo.ts

@@ -14,6 +14,7 @@ import {
     SocketIoPrivateChannel,
 } from './channel';
 import { Connector, PusherConnector, SocketIoConnector, NullConnector } from './connector';
+import { isConstructor } from './util';
 
 /**
  * This class is the primary API for interacting with broadcasting.
@@ -60,8 +61,8 @@ export default class Echo<T extends keyof Broadcaster> {
             this.connector = new SocketIoConnector(this.options);
         } else if (this.options.broadcaster == 'null') {
             this.connector = new NullConnector(this.options);
-        } else if (typeof this.options.broadcaster == 'function') {
-            this.connector = this.options.broadcaster(this.options as EchoOptions<'function'>);
+        } else if (typeof this.options.broadcaster == 'function' && isConstructor(this.options.broadcaster)) {
+            this.connector = new this.options.broadcaster(this.options as EchoOptions<'function'>);
         } else {
             throw new Error(
                 `Broadcaster ${typeof this.options.broadcaster} ${this.options.broadcaster} is not supported.`
@@ -261,11 +262,13 @@ type Broadcaster = {
     };
 };
 
+type Constructor<T = {}> = new (...args: any[]) => T;
+
 type EchoOptions<T extends keyof Broadcaster> = {
     /**
      * The broadcast connector.
      */
-    broadcaster: T extends 'function' ? (options: EchoOptions<T>) => any : T;
+    broadcaster: T extends 'function' ? Constructor<InstanceType<Broadcaster[T]['connector']>> : T;
 
     [key: string]: any;
 };

src/util/index.ts

@@ -1 +1,11 @@
+function isConstructor(obj: any): obj is new (...args: any[]) => any {
+    try {
+        new obj();
+    } catch (err) {
+        if (err.message.includes('is not a constructor')) return false;
+    }
+    return true;
+}
+
+export { isConstructor };
 export * from './event-formatter';

tests/echo.test.ts

@@ -1,4 +1,5 @@
 import Echo from '../src/echo';
+import { NullConnector } from '../src/connector';
 
 describe('Echo', () => {
     test('it will not throw error for supported driver', () => {
@@ -15,7 +16,10 @@ describe('Echo', () => {
         );
 
         expect(() => new Echo({ broadcaster: 'null' })).not.toThrowError('Broadcaster string null is not supported.');
+        expect(() => new Echo({ broadcaster: NullConnector })).not.toThrowError();
 
+        // eslint-disable-next-line
+        // @ts-ignore
         // eslint-disable-next-line @typescript-eslint/no-empty-function
         expect(() => new Echo({ broadcaster: () => {} })).not.toThrowError('Broadcaster function is not supported.');
     });