From 6b7c1b16c94bdef3a3b6ebb20727575654cabc51 Mon Sep 17 00:00:00 2001
From: Project516 <138796702+Project516@users.noreply.github.com>
Date: Sun, 1 Nov 2026 15:48:23 -0600
Subject: [PATCH] Document javaWebWriteStdin and make it require cheerpjInit
 first.

---
 docs/browser.md    | 4 ++++
 src/browser/api.ts | 1 +
 2 files changed, 5 insertions(+)

diff --git a/docs/browser.md b/docs/browser.md
index 956ca8c..0baf24c 100644
--- a/docs/browser.md
+++ b/docs/browser.md
@@ -37,6 +37,10 @@ and `cjFileBlob(path)` also work.
   `/files/uploads/` exists for files the page adds there.
 - The browser console gets whole lines, so two `print` calls and a `println` log one
   line. A partial line is logged after 100 ms.
+- `javaWebWriteStdin(text)` feeds `System.in` (CheerpJ has no such call). A read
+  waits until the page sends text, and text sent before Java reads it is kept.
+  `javaWebWriteStdin(null)` ends the input. Nothing is echoed, so the page shows
+  what the user typed itself.
 
 Library mode calls Java from JS, as in CheerpJ's library mode guide. The VM
 stays up between calls:
diff --git a/src/browser/api.ts b/src/browser/api.ts
index 88b41a9..b8312c5 100644
--- a/src/browser/api.ts
+++ b/src/browser/api.ts
@@ -277,6 +277,7 @@ export function cheerpOSRemoveStringFile(path: string) {
 
 // Feeds System.in; null ends the input.
 export function javaWebWriteStdin(data: string | null) {
+  if (!worker) throw new Error("call cheerpjInit() first");
   send({ type: "stdin", data: data === null ? null : new TextEncoder().encode(data) });
 }