From cc9664ff1b3f265e2e51a8b1fbb7ec324ded3a35 Mon Sep 17 00:00:00 2001
From: Paul Cento <paul.cento@gmail.com>
Date: Fri, 13 Jan 2023 20:36:34 -0500
Subject: [PATCH] `Element.ShadowRoot` returns error when `ShadowRoots` is
 empty (#788)

* Element.ShadowRoot returns an error when ShadowRoots slice is empty

* comment exported ErrNoShadowRoot

* unit test shadow root error

* test shadow root error contains correct error message
---
 element.go      |  3 +++
 element_test.go |  5 +++++
 error.go        | 13 +++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/element.go b/element.go
index f6d6e684..7d1e7da0 100644
--- a/element.go
+++ b/element.go
@@ -402,6 +402,9 @@ func (el *Element) ShadowRoot() (*Element, error) {
 	}
 
 	// though now it's an array, w3c changed the spec of it to be a single.
+	if len(node.ShadowRoots) == 0 {
+		return nil, &ErrNoShadowRoot{el}
+	}
 	id := node.ShadowRoots[0].BackendNodeID
 
 	shadowNode, err := proto.DOMResolveNode{BackendNodeID: id}.Call(el)
diff --git a/element_test.go b/element_test.go
index d560eec0..7dff62bd 100644
--- a/element_test.go
+++ b/element_test.go
@@ -284,6 +284,11 @@ func TestShadowDOM(t *testing.T) {
 		g.mc.stubErr(1, proto.DOMResolveNode{})
 		el.MustShadowRoot()
 	})
+
+	elNoShadow := p.MustElement("script")
+	_, err := elNoShadow.ShadowRoot()
+	g.True((&rod.ErrNoShadowRoot{}).Is(err))
+	g.Has(err.Error(), "element has no shadow root:")
 }
 
 func TestInputTime(t *testing.T) {
diff --git a/error.go b/error.go
index 400e0f1a..ec926551 100644
--- a/error.go
+++ b/error.go
@@ -181,3 +181,16 @@ type ErrPageNotFound struct {
 func (e *ErrPageNotFound) Error() string {
 	return "cannot find page"
 }
+
+// ErrNoShadowRoot error
+type ErrNoShadowRoot struct {
+	*Element
+}
+
+// Error ...
+func (e *ErrNoShadowRoot) Error() string {
+	return fmt.Sprintf("element has no shadow root: %s", e.String())
+}
+
+// Is interface
+func (e *ErrNoShadowRoot) Is(err error) bool { _, ok := err.(*ErrNoShadowRoot); return ok }