Add async function definition for extensions

types/express-graphql/express-graphql-tests.ts

@@ -24,7 +24,8 @@ const graphqlOptionRequestAsync = async (request: express.Request): Promise<grap
     return {
         graphiql: true,
         schema: await Promise.resolve(schema),
-        context: request.session
+        context: request.session,
+        extensions: async (args) => { }
     };
 };
 

types/express-graphql/index.d.ts

@@ -54,7 +54,7 @@ declare namespace graphqlHTTP {
          * An optional function for adding additional metadata to the GraphQL response as a key-value object.
          * The result will be added to "extensions" field in the resulting JSON.
          */
-        extensions?: (args: ExtenstionsArgs) => any;
+        extensions?: ((args: ExtenstionsArgs) => any) | ((args: ExtenstionsArgs) => Promise<any>);
 
     };