3 files changed, 40 insertions, 1 deletions
diff --git a/cli/js/web/body.ts b/cli/js/web/body.ts
index 7a5b63d32..672b7de5a 100644
--- a/cli/js/web/body.ts
+++ b/cli/js/web/body.ts
@@ -2,6 +2,7 @@ import * as blob from "./blob.ts";
 import * as encoding from "./text_encoding.ts";
 import * as domTypes from "./dom_types.d.ts";
 import { ReadableStreamImpl } from "./streams/readable_stream.ts";
+import { isReadableStreamDisturbed } from "./streams/internals.ts";
 import { getHeaderValueParams, hasHeaderValueOf } from "./util.ts";
 import { MultipartParser } from "./fetch/multipart.ts";
 
@@ -116,7 +117,7 @@ export class Body implements domTypes.Body {
   }
 
   get bodyUsed(): boolean {
-    if (this.body && this.body.locked) {
+    if (this.body && isReadableStreamDisturbed(this.body)) {
       return true;
     }
     return false;
diff --git a/cli/js/web/streams/internals.ts b/cli/js/web/streams/internals.ts
index ff8fc25fe..d0d35a1c3 100644
--- a/cli/js/web/streams/internals.ts
+++ b/cli/js/web/streams/internals.ts
@@ -367,6 +367,11 @@ export function isReadableStreamLocked(stream: ReadableStreamImpl): boolean {
   return stream[sym.reader] ? true : false;
 }
 
+export function isReadableStreamDisturbed(stream: ReadableStream): boolean {
+  assert(isReadableStream(stream));
+  return stream[sym.disturbed] ? true : false;
+}
+
 export function isTransformStream(
   x: unknown
 ): x is TransformStreamImpl<any, any> {
diff --git a/cli/tests/unit/fetch_test.ts b/cli/tests/unit/fetch_test.ts
index 57414d652..554cf31e9 100644
--- a/cli/tests/unit/fetch_test.ts
+++ b/cli/tests/unit/fetch_test.ts
@@ -100,6 +100,39 @@ unitTest({ perms: { net: true } }, async function fetchBodyUsed(): Promise<
   assertEquals(response.bodyUsed, true);
 });
 
+unitTest(
+  { perms: { net: true } },
+  async function fetchBodyUsedReader(): Promise<void> {
+    const response = await fetch(
+      "http://localhost:4545/cli/tests/fixture.json"
+    );
+    assert(response.body !== null);
+
+    const reader = response.body.getReader();
+    // Getting a reader should lock the stream but does not consume the body
+    // so bodyUsed should not be true
+    assertEquals(response.bodyUsed, false);
+    reader.releaseLock();
+    await response.json();
+    assertEquals(response.bodyUsed, true);
+  }
+);
+
+unitTest(
+  { perms: { net: true } },
+  async function fetchBodyUsedCancelStream(): Promise<void> {
+    const response = await fetch(
+      "http://localhost:4545/cli/tests/fixture.json"
+    );
+    assert(response.body !== null);
+
+    assertEquals(response.bodyUsed, false);
+    const promise = response.body.cancel();
+    assertEquals(response.bodyUsed, true);
+    await promise;
+  }
+);
+
 unitTest({ perms: { net: true } }, async function fetchAsyncIterator(): Promise<
   void
 > {