From f3e1204fa1eef0cdc46d1d220a96bd7a67ad1f0b Mon Sep 17 00:00:00 2001
From: Karl Seguin <k@openmymind.io>
Date: Mon, 9 Mar 2026 13:44:17 +0800
Subject: [PATCH] Throw exception, as expected, on empty input to
 DOMParser.parseFromString

https://github.com/lightpanda-io/browser/issues/1738
---
 src/browser/tests/domparser.html | 14 +++++++++++---
 src/browser/webapi/DOMParser.zig |  9 +++++----
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/browser/tests/domparser.html b/src/browser/tests/domparser.html
index 70fd6ff9..24d34e89 100644
--- a/src/browser/tests/domparser.html
+++ b/src/browser/tests/domparser.html
@@ -4,9 +4,17 @@
 
 <script id=basic>
 {
-  const parser = new DOMParser();
-  testing.expectEqual('object', typeof parser);
-  testing.expectEqual('function', typeof parser.parseFromString);
+  {
+    const parser = new DOMParser();
+    testing.expectEqual('object', typeof parser);
+    testing.expectEqual('function', typeof parser.parseFromString);
+  }
+
+  {
+    // Empty XML is a parse error (no root element)
+    const parser = new DOMParser();
+    testing.expectError('Error', () => parser.parseFromString('', 'text/xml'));
+  }
 }
 </script>
 
diff --git a/src/browser/webapi/DOMParser.zig b/src/browser/webapi/DOMParser.zig
index e2a0a438..9e27e9c7 100644
--- a/src/browser/webapi/DOMParser.zig
+++ b/src/browser/webapi/DOMParser.zig
@@ -90,15 +90,16 @@ pub fn parseFromString(
                 return pe.err;
             }
 
-            // If first node is a `ProcessingInstruction`, skip it.
             const first_child = doc_node.firstChild() orelse {
-                // Parsing should fail if there aren't any nodes.
-                unreachable;
+                // Empty XML or no root element - this is a parse error.
+                // TODO: Return a document with a <parsererror> element per spec.
+                return error.JsException;
             };
 
+            // If first node is a `ProcessingInstruction`, skip it.
             if (first_child.getNodeType() == 7) {
                 // We're sure that firstChild exist, this cannot fail.
-                _ = doc_node.removeChild(first_child, page) catch unreachable;
+                _ = try doc_node.removeChild(first_child, page);
             }
 
             return doc.asDocument();