2 files changed, 27 insertions, 1 deletions
diff --git a/js/process.ts b/js/process.ts
index bf75b6b32..8ce83477a 100644
--- a/js/process.ts
+++ b/js/process.ts
@@ -83,7 +83,7 @@ export class Process {
   }
 
   /** Buffer the stdout and return it as Uint8Array after EOF.
-   * You must have set stdout to "piped" in when creating the process.
+   * You must set stdout to "piped" when creating the process.
    * This calls close() on stdout after its done.
    */
   async output(): Promise<Uint8Array> {
@@ -97,6 +97,21 @@ export class Process {
     }
   }
 
+  /** Buffer the stderr and return it as Uint8Array after EOF.
+   * You must set stderr to "piped" when creating the process.
+   * This calls close() on stderr after its done.
+   */
+  async stderrOutput(): Promise<Uint8Array> {
+    if (!this.stderr) {
+      throw new Error("Process.stderrOutput: stderr is undefined");
+    }
+    try {
+      return await readAll(this.stderr);
+    } finally {
+      this.stderr.close();
+    }
+  }
+
   close(): void {
     close(this.rid);
   }
diff --git a/js/process_test.ts b/js/process_test.ts
index b442f0092..051841ffe 100644
--- a/js/process_test.ts
+++ b/js/process_test.ts
@@ -187,6 +187,17 @@ testPerm({ run: true }, async function runOutput() {
   p.close();
 });
 
+testPerm({ run: true }, async function runStderrOutput() {
+  const p = run({
+    args: ["python", "-c", "import sys; sys.stderr.write('error')"],
+    stderr: "piped"
+  });
+  const error = await p.stderrOutput();
+  const s = new TextDecoder().decode(error);
+  assertEquals(s, "error");
+  p.close();
+});
+
 testPerm({ run: true }, async function runEnv() {
   const p = run({
     args: [