fix: update streamed code block content

.changeset/fresh-code-blocks-update.md

@@ -0,0 +1,5 @@
+---
+"streamdown": patch
+---
+
+Fix streamed code blocks remaining stale when their content changes without moving in the document.

packages/streamdown/__tests__/code-block-memo.test.tsx

@@ -18,6 +18,30 @@ vi.mock("../lib/code-block", () => ({
 }));
 
 describe("MemoCode in streaming mode", () => {
+  it("should re-render code blocks when their content changes in place", async () => {
+    codeBlockRenderCount = 0;
+
+    const initial = "```js\nfirst\n```";
+    const updated = "```js\nsecond\n```";
+
+    const { container, rerender } = render(<Streamdown>{initial}</Streamdown>);
+
+    await waitFor(() => {
+      expect(container.textContent).toContain("first");
+    });
+
+    const initialRenderCount = codeBlockRenderCount;
+
+    rerender(<Streamdown>{updated}</Streamdown>);
+
+    await waitFor(() => {
+      expect(container.textContent).toContain("second");
+    });
+
+    expect(container.textContent).not.toContain("first");
+    expect(codeBlockRenderCount).toBeGreaterThan(initialRenderCount);
+  });
+
   it("should not re-render unchanged code blocks on streaming updates", async () => {
     codeBlockRenderCount = 0;
 

packages/streamdown/lib/components.tsx

@@ -89,6 +89,38 @@ function sameClassAndNode(
   );
 }
 
+function getCodeContent(children: React.ReactNode): string | undefined {
+  if (typeof children === "string") {
+    return children;
+  }
+
+  if (
+    isValidElement(children) &&
+    children.props &&
+    typeof children.props === "object" &&
+    "children" in children.props &&
+    typeof children.props.children === "string"
+  ) {
+    return children.props.children;
+  }
+
+  return undefined;
+}
+
+function sameCodeContent(
+  prev: React.ReactNode,
+  next: React.ReactNode
+): boolean {
+  const prevContent = getCodeContent(prev);
+  const nextContent = getCodeContent(next);
+
+  if (prevContent === undefined && nextContent === undefined) {
+    return prev === next;
+  }
+
+  return prevContent === nextContent;
+}
+
 const shouldShowControls = (
   config: ControlsConfig,
   type: "table" | "code" | "mermaid" | "image"
@@ -852,19 +884,7 @@ const CodeComponent = ({
     : false;
   const showLineNumbers = !metaNoLineNumbers && contextLineNumbers !== false;
 
-  // Extract code content from children safely
-  let code = "";
-  if (
-    isValidElement(children) &&
-    children.props &&
-    typeof children.props === "object" &&
-    "children" in children.props &&
-    typeof children.props.children === "string"
-  ) {
-    code = children.props.children;
-  } else if (typeof children === "string") {
-    code = children;
-  }
+  const code = getCodeContent(children) ?? "";
 
   if (customRenderer) {
     const CustomComponent = customRenderer.component;
@@ -981,7 +1001,10 @@ const MemoCode = memo<
   DetailedHTMLProps<HTMLAttributes<HTMLElement>, HTMLElement> & ExtraProps
 >(
   CodeComponent,
-  (p, n) => p.className === n.className && sameNodePosition(p.node, n.node)
+  (p, n) =>
+    p.className === n.className &&
+    sameNodePosition(p.node, n.node) &&
+    sameCodeContent(p.children, n.children)
 );
 MemoCode.displayName = "MarkdownCode";