Allow resolver fn to be async

README.md

@@ -16,7 +16,7 @@ You can use it with any GraphQL client and server (not only Apollo).
 
 If you are developing a project that uses this module with TypeScript:
 
-* ensure that your `tsconfig.json` `lib` definition includes `"esnext.asynciterable"`
+* ensure that your `tsconfig.json` `lib` definition includes `"es2018.asynciterable"`
 * `npm install @types/graphql` or `yarn add @types/graphql`
 
 ### Getting started with your first subscription

package.json

@@ -43,7 +43,7 @@
     "sinon": "^6.1.4",
     "sinon-chai": "^3.2.0",
     "tslint": "^5.11.0",
-    "typescript": "^2.3.2"
+    "typescript": "^3.8.3"
   },
   "typings": "dist/index.d.ts",
   "typescript": {

src/test/asyncIteratorSubscription.ts

@@ -133,9 +133,11 @@ describe('GraphQL-JS asyncIterator', () => {
 
     const schema = buildSchema(origIterator, filterFn);
 
-    Promise.resolve(subscribe(schema, query)).then((results: AsyncIterator<ExecutionResult>) => {
+    Promise.resolve(subscribe(schema, query)).then((results: AsyncIterator<ExecutionResult> | ExecutionResult) => {
       expect(isAsyncIterable(results)).to.be.true;
 
+      results = results as AsyncIterator<ExecutionResult>; // above check will fail if not an async iterator
+
       results.next();
       results.return();
 
@@ -190,7 +192,7 @@ let testFiniteAsyncIterator: AsyncIterator<number> = createAsyncIterator([1, 2,
 
 describe('withFilter', () => {
   it('works properly with finite asyncIterators', async () => {
-    let filteredAsyncIterator = withFilter(() => testFiniteAsyncIterator, isEven)();
+    let filteredAsyncIterator = await withFilter(() => testFiniteAsyncIterator, isEven)();
 
     for (let i = 1; i <= 4; i++) {
       let result = await filteredAsyncIterator.next();

src/with-filter.ts

@@ -1,11 +1,11 @@
 import { $$asyncIterator } from 'iterall';
 
 export type FilterFn = (rootValue?: any, args?: any, context?: any, info?: any) => boolean | Promise<boolean>;
-export type ResolverFn = (rootValue?: any, args?: any, context?: any, info?: any) => AsyncIterator<any>;
+export type ResolverFn = (rootValue?: any, args?: any, context?: any, info?: any) => AsyncIterator<any> | Promise<AsyncIterator<any>>;
 
 export const withFilter = (asyncIteratorFn: ResolverFn, filterFn: FilterFn): ResolverFn => {
-  return (rootValue: any, args: any, context: any, info: any): AsyncIterator<any> => {
-    const asyncIterator = asyncIteratorFn(rootValue, args, context, info);
+  return async (rootValue: any, args: any, context: any, info: any): Promise<AsyncIterator<any>> => {
+    const asyncIterator = await asyncIteratorFn(rootValue, args, context, info);
 
     const getNextPromise = () => {
       return asyncIterator
@@ -41,6 +41,6 @@ export const withFilter = (asyncIteratorFn: ResolverFn, filterFn: FilterFn): Res
       [$$asyncIterator]() {
         return this;
       },
-    };
+    } as AsyncIterator<any>; // needed since TS doesn't allow the iterall async iterator symbol
   };
 };