same fix for flatMap

Author: iMoses

lib/internal/streams/operators.js

@@ -232,10 +232,13 @@ async function toArray(options) {
   return result;
 }
 
-async function* flatMap(fn, options) {
-  for await (const val of this.map(fn, options)) {
-    yield* val;
-  }
+function flatMap(fn, options) {
+  const values = this.map(fn, options);
+  return async function* flatMap() {
+    for await (const val of values) {
+      yield* val;
+    }
+  }();
 }
 
 function toIntegerOrInfinity(number) {

test/parallel/test-stream-flatMap.js

@@ -109,20 +109,11 @@ function oneTo5() {
 
 {
   // Error cases
-  assert.rejects(async () => {
-    // eslint-disable-next-line no-unused-vars
-    for await (const unused of Readable.from([1]).flatMap(1));
-  }, /ERR_INVALID_ARG_TYPE/).then(common.mustCall());
-  assert.rejects(async () => {
-    // eslint-disable-next-line no-unused-vars
-    for await (const _ of Readable.from([1]).flatMap((x) => x, {
-      concurrency: 'Foo'
-    }));
-  }, /ERR_OUT_OF_RANGE/).then(common.mustCall());
-  assert.rejects(async () => {
-    // eslint-disable-next-line no-unused-vars
-    for await (const _ of Readable.from([1]).flatMap((x) => x, 1));
-  }, /ERR_INVALID_ARG_TYPE/).then(common.mustCall());
+  assert.throws(() => Readable.from([1]).flatMap(1), /ERR_INVALID_ARG_TYPE/);
+  assert.throws(() => Readable.from([1]).flatMap((x) => x, {
+    concurrency: 'Foo'
+  }), /ERR_OUT_OF_RANGE/);
+  assert.throws(() => Readable.from([1]).flatMap((x) => x, 1), /ERR_INVALID_ARG_TYPE/);
 }
 {
   // Test result is a Readable