From 17c1644d90569aace6b4d2d4ba4d76eada135762 Mon Sep 17 00:00:00 2001
From: Ardis Lu <ardisglu@gmail.com>
Date: Wed, 12 Nov 2025 23:15:55 -0800
Subject: [PATCH] Loosen type definition to `AsyncIterable`

This change reflects the actual runtime check that is being performed (i.e., that `Symbol.asyncIterator` is implemented) and allows users to pass (runtime-valid) `async function*` transformation functions without any type errors.
---
 src/core.js       |  8 ++++----
 test/core.test.js | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/core.js b/src/core.js
index ce917f8..53bb1c3 100644
--- a/src/core.js
+++ b/src/core.js
@@ -230,14 +230,14 @@ export class CSVReader {
  * A function to process a row of CSV data from `CSVReader`.
  * @callback TransformationFunction
  * @param {Array<any>} row A row of input CSV data before transformation.
- * @returns {MaybePromise<TransformationOutput|ReadableStream<TransformationOutput>>}
+ * @returns {MaybePromise<TransformationOutput|AsyncIterable<TransformationOutput>>}
  */
 
 /**
  * A function to process multiple rows of CSV data from `CSVReader`.
  * @callback TransformationFunctionBatch
  * @param {Array<Array<any>>} rows Multiple rows of input CSV data.
- * @returns {MaybePromise<TransformationOutput|ReadableStream<TransformationOutput>>}
+ * @returns {MaybePromise<TransformationOutput|AsyncIterable<TransformationOutput>>}
  */
 
 /**
@@ -246,7 +246,7 @@ export class CSVReader {
  * @param {Array<any>} row The row passed to the transformation function which threw the error.
  * @param {Error} error The error thrown by the transformation function.
  * @param {TransformationFunction} fn The transformation function itself. This argument can be used to retry a transformation.
- * @returns {MaybePromise<TransformationOutput|ReadableStream<TransformationOutput>>}
+ * @returns {MaybePromise<TransformationOutput|AsyncIterable<TransformationOutput>>}
  */
 
 /**
@@ -255,7 +255,7 @@ export class CSVReader {
  * @param {Array<Array<any>>} rows The rows of input CSV data passed to the transformation function which threw the error.
  * @param {Error} error The error thrown by the transformation function.
  * @param {TransformationFunctionBatch} fn The transformation function itself. This argument can be used to retry a transformation.
- * @returns {MaybePromise<TransformationOutput|ReadableStream<TransformationOutput>>}
+ * @returns {MaybePromise<TransformationOutput|AsyncIterable<TransformationOutput>>}
  */
 
 /**
diff --git a/test/core.test.js b/test/core.test.js
index 9bd6c0b..0f8ac08 100644
--- a/test/core.test.js
+++ b/test/core.test.js
@@ -582,6 +582,27 @@ suite('CSVTransformer', { concurrency: true }, () => {
       ]));
     deepStrictEqual(fn.mock.callCount(), 2);
   });
+  test('handles AsyncGenerator (async function*)', { concurrency: true }, async (t) => {
+    await createCSVMockStream([
+      ['columnA'],
+      ['1'],
+      ['2']
+    ])
+      .pipeThrough(new CSVTransformer(async function* (row) {
+        yield [`${row[0]}a`];
+        yield [`${row[0]}b`];
+        yield [`${row[0]}c`];
+      }))
+      .pipeTo(csvStreamEqualWritable([
+        ['columnA'],
+        ['1a'],
+        ['1b'],
+        ['1c'],
+        ['2a'],
+        ['2b'],
+        ['2c']
+      ]));
+  });
   test('handles ReadableStream', { concurrency: true }, async (t) => {
     await createCSVMockStream([
       ['columnA'],
-- 
2.47.3