1 files changed, 26 insertions, 0 deletions
diff --git a/testing/web-platform/tests/html/dom/elements/global-attributes/dataset-prototype.html b/testing/web-platform/tests/html/dom/elements/global-attributes/dataset-prototype.html
new file mode 100644
index 0000000000..6b16618461
--- /dev/null
+++ b/testing/web-platform/tests/html/dom/elements/global-attributes/dataset-prototype.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Dataset - element.dataset is an instance of DOMStringMap</title>
+    <script src="/resources/testharness.js"></script>
+    <script src="/resources/testharnessreport.js"></script>
+  </head>
+  <body>
+    <h1>Dataset - element.dataset is an instance of DOMStringMap</h1>
+    <div id="log"></div>
+    <script>
+      test(function() { assert_true(document.createElement("div").dataset instanceof window.DOMStringMap); },
+        "An elements dataset property is an instance of a DOMStringMap");
+      test(function() {
+        var dataset = document.createElement("div").dataset;
+        assert_true("toString" in dataset, '"toString" in dataset');
+        assert_equals(dataset.toString, Object.prototype.toString);
+        assert_false("expando" in dataset, '"expando" in dataset');
+        assert_equals(dataset.expando, undefined);
+        Object.prototype.expando = 42;
+        assert_true("expando" in dataset, '"expando" in dataset');
+        assert_equals(dataset.expando, 42);
+      }, "Properties on Object.prototype should shine through.");
+    </script>
+  </body>
+</html>