From 6d4966e83dc12387e3abc331ce51efebc8631be3 Mon Sep 17 00:00:00 2001
From: Pierre Tachoire <pierre@lightpanda.io>
Date: Sat, 13 Dec 2025 14:05:05 +0100
Subject: [PATCH] implement document.write

---
 src/browser/dom/document.zig      | 59 +++++++++++++++++++++++++++++++
 src/browser/page.zig              |  4 +++
 src/tests/dom/document_write.html | 25 +++++++++++++
 3 files changed, 88 insertions(+)
 create mode 100644 src/tests/dom/document_write.html

diff --git a/src/browser/dom/document.zig b/src/browser/dom/document.zig
index db675aea..7763cd3e 100644
--- a/src/browser/dom/document.zig
+++ b/src/browser/dom/document.zig
@@ -319,9 +319,68 @@ pub const Document = struct {
         log.debug(.web_api, "not implemented", .{ .feature = "Document hasFocus" });
         return true;
     }
+
+    pub fn _open(_: *parser.Document, page: *Page) !*parser.DocumentHTML {
+        if (page.open) {
+            return page.window.document;
+        }
+
+        // This implementation is invalid.
+        // According to MDN, we should cleanup registered listeners.
+        // So we sould cleanup previous DOM memory.
+        // But this implementation is more simple for now.
+        const html_doc = try parser.documentHTMLParseFromStr("");
+        try page.setDocument(html_doc);
+        page.open = true;
+
+        return page.window.document;
+    }
+
+    pub fn _close(_: *parser.Document, page: *Page) !void {
+        page.open = false;
+    }
+
+    pub fn _write(self: *parser.Document, str: []const u8, page: *Page) !void {
+        if (!page.open) {
+            _ = try _open(self, page);
+        }
+        const document = parser.documentHTMLToDocument(page.window.document);
+        const fragment = try parser.documentParseFragmentFromStr(document, str);
+        const fragment_node = parser.documentFragmentToNode(fragment);
+
+        const fragment_html = parser.nodeFirstChild(fragment_node) orelse return;
+        const fragment_head = parser.nodeFirstChild(fragment_html) orelse return;
+        const fragment_body = parser.nodeNextSibling(fragment_head) orelse return;
+
+        const document_node = parser.documentToNode(document);
+        const document_html = parser.nodeFirstChild(document_node) orelse return;
+        const document_head = parser.nodeFirstChild(document_html) orelse return;
+        const document_body = parser.nodeNextSibling(document_head) orelse return;
+
+        {
+            const children = try parser.nodeGetChildNodes(fragment_head);
+            // always index 0, because nodeAppendChild moves the node out of
+            // the nodeList and into the new tree
+            while (parser.nodeListItem(children, 0)) |child| {
+                _ = try parser.nodeAppendChild(document_head, child);
+            }
+        }
+
+        {
+            const children = try parser.nodeGetChildNodes(fragment_body);
+            // always index 0, because nodeAppendChild moves the node out of
+            // the nodeList and into the new tree
+            while (parser.nodeListItem(children, 0)) |child| {
+                _ = try parser.nodeAppendChild(document_body, child);
+            }
+        }
+    }
 };
 
 const testing = @import("../../testing.zig");
 test "Browser: DOM.Document" {
     try testing.htmlRunner("dom/document.html");
 }
+test "Browser: DOM.Document.write" {
+    try testing.htmlRunner("dom/document_write.html");
+}
diff --git a/src/browser/page.zig b/src/browser/page.zig
index e33e1c7a..c3869803 100644
--- a/src/browser/page.zig
+++ b/src/browser/page.zig
@@ -103,6 +103,10 @@ pub const Page = struct {
     notified_network_idle: IdleNotification = .init,
     notified_network_almost_idle: IdleNotification = .init,
 
+    // Indicates if the page's document is open or close.
+    // Relates with https://developer.mozilla.org/en-US/docs/Web/API/Document/open
+    open: bool = false,
+
     const Mode = union(enum) {
         pre: void,
         err: anyerror,
diff --git a/src/tests/dom/document_write.html b/src/tests/dom/document_write.html
new file mode 100644
index 00000000..7d004981
--- /dev/null
+++ b/src/tests/dom/document_write.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+
+<div id="content">
+  <a id="a1" href="foo" class="ok">OK</a>
+  <p id="p1" class="ok empty">
+    <span id="s1"></span>
+  </p>
+  <p id="p2"> And</p>
+</div>
+
+
+<script id=document_write>
+  document.open();
+  document.write("<p id=ok>Hello world!</p>");
+  document.write("<p>I am a fish</p>");
+  document.write("<p>The number is 42</p>");
+  document.close();
+
+  const ok = document.getElementById("ok");
+  testing.expectEqual('Hello world!', ok.innerText);
+
+  const content = document.firstElementChild.innerHTML;
+  testing.expectEqual('<head></head><body><p id="ok">Hello world!</p><p>I am a fish</p><p>The number is 42</p></body>', content);
+</script>