make initialize return a Promise (#328)

closes #152

Author: luca-peruzzo

src/definitions.ts

@@ -143,7 +143,7 @@ export interface GoogleAuthPlugin {
    * @param options - Optional initialization options.
    * @since 3.1.0
    */
-  initialize(options?: InitOptions): void;
+  initialize(options?: InitOptions): Promise<void>;
 
   /**
    * Initiates the sign-in process and returns a Promise that resolves with the user information.

src/web.ts

@@ -39,7 +39,7 @@ export class GoogleAuthWeb extends WebPlugin implements GoogleAuthPlugin {
       scopes: [],
       grantOfflineAccess: false,
     }
-  ) {
+  ): Promise<void> {
     if (typeof window === 'undefined') {
       return;
     }
@@ -64,6 +64,7 @@ export class GoogleAuthWeb extends WebPlugin implements GoogleAuthPlugin {
     });
 
     this.addUserChangeListener();
+    return this.gapiLoaded;
   }
 
   platformJsLoaded() {